diff --git a/doc/XMLreference.rst b/doc/XMLreference.rst
index b605c1dc..b8e1b949 100644
--- a/doc/XMLreference.rst
+++ b/doc/XMLreference.rst
@@ -3346,7 +3346,7 @@ coordinates results in compiler error. See :ref:`CComposite` in the modeling gui
 .. _body-composite-vertex:
 
 :at:`vertex`: :at-val:`real(3*nvert), optional`
-   Vertex 3D positions in global coordinates (cable only).
+   Vertex 3D positions in global coordinates (cable and shell).
 
 .. _body-composite-face:
 
diff --git a/doc/changelog.rst b/doc/changelog.rst
index 20e8110c..988c1ef5 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -31,27 +31,38 @@ New features
 3. Added :ref:`mjThreadPool` and :ref:`mjTask` which allow for multi-threaded operations within the MuJoCo engine
    pipeline.
 
+.. youtube:: ra2bTiZHGlw
+   :align: right
+   :width: 240px
+
+4. Added capability to initialize :ref:`composite<body-composite>` particles with arbitrary positions.
+
+5. Added `shell <https://github.com/deepmind/mujoco/blob/main/plugin/elasticity/shell.cc>`_ passive force plugin:
+
+   - Collisions use spheres located at mesh vertices.
+   - Stretching as tendon constraints and bending using a constant precomputed Hessian (cotangent operator).
+
 General
 ^^^^^^^
 
 .. admonition:: Breaking API changes
    :class: attention
 
-   4. Removed the macros ``mjMARKSTACK`` and ``mjFREESTACK``.
+   6. Removed the macros ``mjMARKSTACK`` and ``mjFREESTACK``.
 
       **Migration:** These macros have been replaced by new functions :ref:`mj_markStack` and
       :ref:`mj_freeStack`. These functions manage the :ref:`mjData stack<siStack>` in a fully encapsulated way (i.e.,
       without introducing a local variable at the call site).
 
-   5. Renamed ``mj_stackAlloc`` to :ref:`mj_stackAllocNum`. The new function :ref:`mj_stackAllocByte` allocates an
+   7. Renamed ``mj_stackAlloc`` to :ref:`mj_stackAllocNum`. The new function :ref:`mj_stackAllocByte` allocates an
       arbitrary number of bytes and has an additional argument for specifying the alignment of the returned pointer.
 
       **Migration:** The functionality for allocating ``mjtNum`` arrays is now available via :ref:`mj_stackAllocNum`.
 
-   6. Renamed the ``nstack`` field in :ref:`mjModel` and :ref:`mjData` to ``narena``. Changed ``narena``, ``pstack``,
+   8. Renamed the ``nstack`` field in :ref:`mjModel` and :ref:`mjData` to ``narena``. Changed ``narena``, ``pstack``,
       and ``maxuse_stack`` to count number of bytes rather than number of :ref:`mjtNum` |-| s.
 
-   7. Changed :ref:`mjData.solver<mjData>`, the array used to collect solver diagnostic information.
+   9. Changed :ref:`mjData.solver<mjData>`, the array used to collect solver diagnostic information.
       This array of :ref:`mjSolverStat` structs is now of length ``mjNISLAND * mjNSOLVER``, interpreted as as a matrix.
       Each row of length ``mjNSOLVER`` contains separate solver statistics for each constraint island.
       If the solver does not use islands, only row 0 is filled.
@@ -62,46 +73,46 @@ General
       - Renamed ``mjData.solver_iter`` to ``solver_niter``. Both this member and ``mjData.solver_nnz`` are now integer
         vectors of length ``mjNISLAND``.
 
-   8. Removed ``mjOption.collision`` and the associated ``option/collision`` attribute.
+   10. Removed ``mjOption.collision`` and the associated ``option/collision`` attribute.
 
-      **Migration:**
+       **Migration:**
 
-      - For models which have ``<option collision="all"/>``, delete the attribute.
-      - For models which have ``<option collision="dynamic"/>``, delete all :ref:`pair<contact-pair>` elements.
-      - For models which have ``<option collision="pair"/>``, disable all dynamic collisions (determined
-        via contype/conaffinity) by first deleting all :ref:`contype<body-geom-contype>` and
-        :ref:`conaffinity<body-geom-conaffinity>` attributes in the model and then setting them globally to ``0`` using
-        |br| ``<default> <geom contype="0" conaffinity="0"/> </default>``.
+       - For models which have ``<option collision="all"/>``, delete the attribute.
+       - For models which have ``<option collision="dynamic"/>``, delete all :ref:`pair<contact-pair>` elements.
+       - For models which have ``<option collision="pair"/>``, disable all dynamic collisions (determined
+         via contype/conaffinity) by first deleting all :ref:`contype<body-geom-contype>` and
+         :ref:`conaffinity<body-geom-conaffinity>` attributes in the model and then setting them globally to ``0`` using
+         |br| ``<default> <geom contype="0" conaffinity="0"/> </default>``.
 
-9. Added a new :ref:`dyntype<actuator-general-dyntype>`, ``filterexact``, which updates first-order filter states with
-   the exact formula rather than with Euler integration.
-10. Added an actuator attribute, :ref:`actearly<actuator-general-actearly>`, which uses semi-implicit integration for
+11. Added a new :ref:`dyntype<actuator-general-dyntype>`, ``filterexact``, which updates first-order filter states with
+    the exact formula rather than with Euler integration.
+12. Added an actuator attribute, :ref:`actearly<actuator-general-actearly>`, which uses semi-implicit integration for
     actuator forces: using the next step's actuator state to compute the current actuator forces at the current timestep.
-11. Renamed ``actuatorforcerange`` and ``actuatorforcelimited``, introduced in the previous version to
+13. Renamed ``actuatorforcerange`` and ``actuatorforcelimited``, introduced in the previous version to
     :ref:`actuatorfrcrange<body-joint-actuatorfrcrange>` and
     :ref:`actuatorfrclimited<body-joint-actuatorfrclimited>`, respectively.
-12. Added the flag :ref:`eulerdamp<option-flag-eulerdamp>`, which disables implicit integration of joint damping in the
+14. Added the flag :ref:`eulerdamp<option-flag-eulerdamp>`, which disables implicit integration of joint damping in the
     Euler integrator. See the :ref:`Numerical Integration<geIntegration>` section for more details.
-13. Added the flag :ref:`invdiscrete<option-flag-invdiscrete>`, which enables discrete-time inverse dynamics for all
+15. Added the flag :ref:`invdiscrete<option-flag-invdiscrete>`, which enables discrete-time inverse dynamics for all
     :ref:`integrators<option-integrator>` other than ``RK4``. See the flag documentation for more details.
-14. Added :ref:`ls_iterations<option-ls_iterations>` and :ref:`ls_tolerance<option-ls_tolerance>` options for adjusting
+16. Added :ref:`ls_iterations<option-ls_iterations>` and :ref:`ls_tolerance<option-ls_tolerance>` options for adjusting
     linesearch stopping criteria in CG and Newton solvers. These can be useful for performance tuning.
-15. Added ``mesh_pos`` and ``mesh_quat`` fields to :ref:`mjModel` to store the normalizing transformation applied to
+17. Added ``mesh_pos`` and ``mesh_quat`` fields to :ref:`mjModel` to store the normalizing transformation applied to
     mesh assets. Fixes `#409 <https://github.com/google-deepmind/mujoco/issues/409>`__ .
-16. Added camera :ref:`resolution<body-camera-resolution>` attribute and :ref:`camprojection<sensor-camprojection>`
+18. Added camera :ref:`resolution<body-camera-resolution>` attribute and :ref:`camprojection<sensor-camprojection>`
     sensor. If camera resolution is set to positive values, the camera projection sensor will report the location of a
     target site, projected onto the camera image, in pixel coordinates.
 
 Python bindings
 ^^^^^^^^^^^^^^^
 
-17. Fixed `#870 <https://github.com/google-deepmind/mujoco/issues/870>`__ where calling ``update_scene`` with an invalid
+19. Fixed `#870 <https://github.com/google-deepmind/mujoco/issues/870>`__ where calling ``update_scene`` with an invalid
     camera name used the default camera.
 
 Bug fixes
 ^^^^^^^^^
 
-18. Fixed a bug that was causing :ref:`geom margin<body-geom-margin>` to be ignored during the construction of
+20. Fixed a bug that was causing :ref:`geom margin<body-geom-margin>` to be ignored during the construction of
     midphase collision trees.
 
 
diff --git a/model/plugin/elasticity/mannequin.xml b/model/plugin/elasticity/mannequin.xml
new file mode 100644
index 00000000..ad036287
--- /dev/null
+++ b/model/plugin/elasticity/mannequin.xml
@@ -0,0 +1,171 @@
+<!-- Copyright 2021 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Mannequin">
+  <!-- Static humanoid model with all joints removed -->
+  <option timestep="0.005"/>
+
+  <visual>
+    <map force="0.1" zfar="30"/>
+    <rgba haze="0.15 0.25 0.35 1"/>
+    <global offwidth="2560" offheight="1440" elevation="-20" azimuth="120"/>
+  </visual>
+
+  <statistic center="0 0 0.7"/>
+
+  <asset>
+    <texture type="skybox" builtin="gradient" rgb1=".3 .5 .7" rgb2="0 0 0" width="32" height="512"/>
+    <texture name="body" type="cube" builtin="flat" mark="cross" width="128" height="128" rgb1="0.8 0.6 0.4" rgb2="0.8 0.6 0.4" markrgb="1 1 1" random="0.01"/>
+    <material name="body" texture="body" texuniform="true" rgba="0.8 0.6 .4 1"/>
+    <texture name="grid" type="2d" builtin="checker" width="512" height="512" rgb1=".1 .2 .3" rgb2=".2 .3 .4"/>
+    <material name="grid" texture="grid" texrepeat="1 1" texuniform="true" reflectance=".2"/>
+  </asset>
+
+  <default>
+    <motor ctrlrange="-1 1" ctrllimited="true"/>
+    <default class="body">
+
+      <!-- geoms -->
+      <geom type="capsule" condim="1" friction=".7" solimp=".9 .99 .003" solref=".015 1" material="body"/>
+      <default class="thigh">
+        <geom size=".06"/>
+      </default>
+      <default class="shin">
+        <geom fromto="0 0 0 0 0 -.3"  size=".049"/>
+      </default>
+      <default class="foot">
+        <geom size=".027"/>
+        <default class="foot1">
+          <geom fromto="-.07 -.01 0 .14 -.03 0"/>
+        </default>
+        <default class="foot2">
+          <geom fromto="-.07 .01 0 .14  .03 0"/>
+        </default>
+      </default>
+      <default class="arm_upper">
+        <geom size=".04"/>
+      </default>
+      <default class="arm_lower">
+        <geom size=".031"/>
+      </default>
+      <default class="hand">
+        <geom type="sphere" size=".04"/>
+      </default>
+
+      <!-- joints -->
+      <joint type="hinge" damping=".2" stiffness="1" armature=".01" limited="true" solimplimit="0 .99 .01"/>
+      <default class="joint_big">
+        <joint damping="5" stiffness="10"/>
+        <default class="hip_x">
+          <joint range="-30 10"/>
+        </default>
+        <default class="hip_z">
+          <joint range="-60 35"/>
+        </default>
+        <default class="hip_y">
+          <joint axis="0 1 0" range="-150 20"/>
+        </default>
+        <default class="joint_big_stiff">
+          <joint stiffness="20"/>
+        </default>
+      </default>
+      <default class="knee">
+        <joint pos="0 0 .02" axis="0 -1 0" range="-160 2"/>
+      </default>
+      <default class="ankle">
+        <joint range="-50 50"/>
+        <default class="ankle_y">
+          <joint pos="0 0 .08" axis="0 1 0" stiffness="6"/>
+        </default>
+        <default class="ankle_x">
+          <joint pos="0 0 .04" stiffness="3"/>
+        </default>
+      </default>
+      <default class="shoulder">
+        <joint range="-85 60"/>
+      </default>
+      <default class="elbow">
+        <joint range="-100 50" stiffness="0"/>
+      </default>
+    </default>
+  </default>
+
+  <worldbody>
+    <geom name="floor" size="0 0 .05" type="plane" material="grid" condim="3"/>
+    <light name="spotlight" mode="targetbodycom" target="torso" diffuse=".8 .8 .8" specular="0.3 0.3 0.3" pos="0 -6 4" cutoff="30"/>
+    <body name="torso" pos="0 0 1.282" childclass="body">
+      <light name="top" pos="0 0 2" mode="trackcom"/>
+      <camera name="back" pos="-3 0 1" xyaxes="0 -1 0 1 0 2" mode="trackcom"/>
+      <camera name="side" pos="0 -3 1" xyaxes="1 0 0 0 1 2" mode="trackcom"/>
+      <freejoint name="root"/>
+      <geom name="torso" fromto="0 -.07 0 0 .07 0" size=".07"/>
+      <geom name="waist_upper" fromto="-.01 -.06 -.12 -.01 .06 -.12" size=".06"/>
+      <body name="head" pos="0 0 .19">
+        <geom name="head" type="sphere" size=".09"/>
+        <camera name="egocentric" pos=".09 0 0" xyaxes="0 -1 0 .1 0 1" fovy="80"/>
+      </body>
+      <body name="waist_lower" pos="-.01 0 -.26">
+        <geom name="waist_lower" fromto="0 -.06 0 0 .06 0" size=".06"/>
+        <body name="pelvis" pos="0 0 -.165">
+          <geom name="butt" fromto="-.02 -.07 0 -.02 .07 0" size=".09"/>
+          <body name="thigh_right" pos="0 -.1 -.04">
+            <geom name="thigh_right" fromto="0 0 0 0 .01 -.34" class="thigh"/>
+            <body name="shin_right" pos="0 .01 -.4">
+              <geom name="shin_right" class="shin"/>
+              <body name="foot_right" pos="0 0 -.39">
+                <geom name="foot1_right" class="foot1"/>
+                <geom name="foot2_right" class="foot2"/>
+              </body>
+            </body>
+          </body>
+          <body name="thigh_left" pos="0 .1 -.04">
+            <geom name="thigh_left" fromto="0 0 0 0 -.01 -.34" class="thigh"/>
+            <body name="shin_left" pos="0 -.01 -.4">
+              <geom name="shin_left" fromto="0 0 0 0 0 -.3" class="shin"/>
+              <body name="foot_left" pos="0 0 -.39">
+                <geom name="foot1_left" class="foot1"/>
+                <geom name="foot2_left" class="foot2"/>
+              </body>
+            </body>
+          </body>
+        </body>
+      </body>
+      <body name="upper_arm_right" pos="0 -.17 .06">
+        <geom name="upper_arm_right" fromto="0 0 0 0 -.22 0" class="arm_upper"/>
+        <body name="lower_arm_right" pos="0 -.22 0">
+          <geom name="lower_arm_right" fromto=".01 .01 .01 0 -.21 -.05" class="arm_lower"/>
+          <body name="hand_right" pos="0 -.22 -.05">
+            <geom name="hand_right" zaxis="1 1 1" class="hand"/>
+          </body>
+        </body>
+      </body>
+      <body name="upper_arm_left" pos="0 .17 .06">
+        <geom name="upper_arm_left" fromto="0 0 0 0 .22 0" class="arm_upper"/>
+        <body name="lower_arm_left" pos="0 .22 0">
+          <geom name="lower_arm_left" fromto=".01 -.01 .01 0 .21 -.05" class="arm_lower"/>
+          <body name="hand_left" pos="0 .22 -.05">
+            <geom name="hand_left" zaxis="1 -1 1" class="hand"/>
+          </body>
+        </body>
+      </body>
+    </body>
+  </worldbody>
+
+  <contact>
+    <exclude body1="waist_lower" body2="thigh_right"/>
+    <exclude body1="waist_lower" body2="thigh_left"/>
+  </contact>
+
+</mujoco>
diff --git a/model/plugin/elasticity/plate.xml b/model/plugin/elasticity/plate.xml
new file mode 100644
index 00000000..6b742c31
--- /dev/null
+++ b/model/plugin/elasticity/plate.xml
@@ -0,0 +1,54 @@
+<!-- Copyright 2021 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Plate">
+  <include file="scene.xml"/>
+
+  <extension>
+    <plugin plugin="mujoco.elasticity.shell"/>
+  </extension>
+
+  <option solver="CG" tolerance="1e-6"/>
+
+  <size memory="10M"/>
+
+  <visual>
+    <map stiffness="100"/>
+  </visual>
+
+  <default>
+    <default class="wall">
+      <geom type="plane" size=".5 .5 .05"/>
+    </default>
+  </default>
+
+  <worldbody>
+    <body mocap="true" pos="-.1 .05 0" zaxis=".5 0 1">
+      <geom type="capsule" size=".1 .1" group="1"/>
+    </body>
+    <composite type="particle" count="16 16 1" spacing="0.05" offset="0 0 1">
+      <geom size=".02" rgba=".8 .2 .1 1" group="4" density="1000"
+            condim="3" solref="0.01 1" solimp=".95 .99 .0001"/>
+      <skin inflate="0.01" rgba=".4 0 .3 1" subgrid="4"/>
+      <plugin plugin="mujoco.elasticity.shell">
+        <config key="poisson" value="0"/>
+        <config key="damping" value="0.001"/>
+        <config key="thickness" value="1e-2"/>
+        <!--Units are in Pa (SI)-->
+        <config key="young" value="3e7"/>
+      </plugin>
+    </composite>
+  </worldbody>
+</mujoco>
diff --git a/model/plugin/elasticity/poncho.xml b/model/plugin/elasticity/poncho.xml
new file mode 100644
index 00000000..859bf95d
--- /dev/null
+++ b/model/plugin/elasticity/poncho.xml
@@ -0,0 +1,1417 @@
+<!-- Copyright 2023 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Poncho">
+  <include file="mannequin.xml"/>
+
+  <option solver="CG" tolerance="1e-6" timestep="0.004"/>
+
+  <size memory="50M"/>
+
+  <extension>
+    <plugin plugin="mujoco.elasticity.shell"/>
+  </extension>
+
+  <worldbody>
+    <composite type="particle" offset="0 0 2" vertex="
+      -1 1 0
+      -0.875 1 0
+      -0.833333333333 0.91666666513 0
+      -1 0.875 0
+      -0.916666667179 0.833333331284 0
+      -0.812500001409 0.81249999936 0
+      -0.750000001537 0.749999999488 0
+      -0.75 1 0
+      -0.718750000576 0.906249998143 0
+      -1 0.75 0
+      -0.906250000192 0.718749998527 0
+      -0.833333333333 0.666666665642 0
+      -0.734187703053 0.642350849083 0
+      -0.666666667691 0.833333331284 0
+      -0.612946163782 0.7237083968 0
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+      0 1 0
+      -1.02445474326e-09 0.771816853128 0
+      -1.02445474326e-09 0.881970586611 0
+      -0.1205911549 0.389682708205 0
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+      -0.523096782922 0.0704802950569 0
+      -0.474500356218 0.138575492276 0
+      -0.360272421185 0.185875041118 0
+      -0.290000784015 0.151369611594 0
+      -0.186173128789 0.255202155519 0
+      -0.222463263127 0.16894673637 0
+      -0.125413489179 0.290004062271 0
+      -1 0 0
+      -0.88197058866 -1.02445474326e-09 0
+      -0.771816855177 -1.02445474326e-09 0
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+      402 419 401
+      398 399 418
+      398 376 378">
+      <geom size=".02" rgba=".8 .2 .1 1" group="4" density="1000"
+            condim="3" solref="0.01 1" solimp=".95 .99 .0001"/>
+      <skin inflate="0.001" rgba=".4 0 .3 1"/>
+      <plugin plugin="mujoco.elasticity.shell">
+        <config key="poisson" value="0"/>
+        <config key="damping" value="0.001"/>
+        <config key="thickness" value="8e-3"/>
+        <!--Units are in Pa (SI)-->
+        <config key="young" value="3e7"/>
+      </plugin>
+    </composite>
+  </worldbody>
+</mujoco>
diff --git a/plugin/elasticity/CMakeLists.txt b/plugin/elasticity/CMakeLists.txt
index 81946e9a..833e0c16 100644
--- a/plugin/elasticity/CMakeLists.txt
+++ b/plugin/elasticity/CMakeLists.txt
@@ -22,6 +22,8 @@ set(MUJOCO_ELASTICITY_SRCS
     elasticity.cc
     elasticity.h
     register.cc
+    shell.cc
+    shell.h
     solid.cc
     solid.h
 )
diff --git a/plugin/elasticity/register.cc b/plugin/elasticity/register.cc
index e349379f..c3747200 100644
--- a/plugin/elasticity/register.cc
+++ b/plugin/elasticity/register.cc
@@ -14,12 +14,14 @@
 
 #include <mujoco/mjplugin.h>
 #include "cable.h"
+#include "shell.h"
 #include "solid.h"
 
 namespace mujoco::plugin::elasticity {
 
 mjPLUGIN_LIB_INIT {
   Cable::RegisterPlugin();
+  Shell::RegisterPlugin();
   Solid::RegisterPlugin();
 }
 
diff --git a/plugin/elasticity/shell.cc b/plugin/elasticity/shell.cc
new file mode 100644
index 00000000..8c671436
--- /dev/null
+++ b/plugin/elasticity/shell.cc
@@ -0,0 +1,305 @@
+// Copyright 2023 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <algorithm>
+#include <cctype>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <functional>
+#include <sstream>
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+#include <mujoco/mjplugin.h>
+#include <mujoco/mjtnum.h>
+#include <mujoco/mujoco.h>
+#include "shell.h"
+
+
+namespace mujoco::plugin::elasticity {
+namespace {
+
+// local tetrahedron numbering
+constexpr int kNumEdges = Stencil2D::kNumEdges;
+constexpr int kNumVerts = Stencil2D::kNumVerts;
+constexpr int edge[kNumEdges][2] = {{1, 2}, {2, 0}, {0, 1}};
+
+// copied from void mjXUtil
+void String2Vector(const std::string& txt, std::vector<int>& vec) {
+  std::stringstream strm(txt);
+  vec.clear();
+
+  while (!strm.eof()) {
+    int num;
+    strm >> num;
+    if (strm.fail()) {
+      break;
+    } else {
+      vec.push_back(num);
+    }
+  }
+}
+
+// cotangent between two edges
+mjtNum cot(mjtNum* x, int v0, int v1, int v2) {
+  mjtNum normal[3];
+  mjtNum edge1[3];
+  mjtNum edge2[3];
+
+  mju_sub3(edge1, x+3*v1, x+3*v0);
+  mju_sub3(edge2, x+3*v2, x+3*v0);
+  mju_cross(normal, edge1, edge2);
+
+  return mju_dot3(edge1, edge2) / mju_norm3(normal);
+}
+
+// area of a triangle
+mjtNum ComputeVolume(const mjtNum* x, const int v[kNumVerts]) {
+  mjtNum normal[3];
+  mjtNum edge1[3];
+  mjtNum edge2[3];
+
+  mju_sub3(edge1, x+3*v[1], x+3*v[0]);
+  mju_sub3(edge2, x+3*v[2], x+3*v[0]);
+  mju_cross(normal, edge1, edge2);
+
+  return mju_norm3(normal) / 2;
+}
+
+// reads numeric attributes
+bool CheckAttr(const char* name, const mjModel* m, int instance) {
+  char* end;
+  std::string value = mj_getPluginConfig(m, instance, name);
+  value.erase(std::remove_if(value.begin(), value.end(), isspace), value.end());
+  strtod(value.c_str(), &end);
+  return end == value.data() + value.size();
+}
+
+struct PairHash
+{
+    template <class T1, class T2>
+    std::size_t operator() (const std::pair<T1, T2>& pair) const {
+        return std::hash<T1>()(pair.first) ^ std::hash<T2>()(pair.second);
+    }
+};
+
+}  // namespace
+
+// factory function
+std::optional<Shell> Shell::Create(const mjModel* m, mjData* d, int instance) {
+    if (CheckAttr("face", m, instance) &&
+        CheckAttr("poisson", m, instance) &&
+        CheckAttr("young", m, instance) &&
+        CheckAttr("thickness", m, instance)) {
+      mjtNum nu = strtod(mj_getPluginConfig(m, instance, "poisson"), nullptr);
+      mjtNum E = strtod(mj_getPluginConfig(m, instance, "young"), nullptr);
+      mjtNum thick =
+          strtod(mj_getPluginConfig(m, instance, "thickness"), nullptr);
+      mjtNum damp =
+          strtod(mj_getPluginConfig(m, instance, "damping"), nullptr);
+      std::vector<int> face;
+      String2Vector(mj_getPluginConfig(m, instance, "face"), face);
+      return Shell(m, d, instance, nu, E, damp, thick, face);
+    } else {
+      mju_warning("Invalid parameter specification in shell plugin");
+      return std::nullopt;
+    }
+}
+
+// create map from triangles to vertices and edges and from edges to vertices
+void Shell::CreateStencils(const std::vector<int>& face) {
+  // populate stencil
+  nt = face.size() / kNumVerts;
+  elements.resize(nt);
+  for (int t = 0; t < nt; t++) {
+    for (int v = 0; v < kNumVerts; v++) {
+      elements[t].vertices[v] = face[kNumVerts*t+v]-1;
+    }
+  }
+
+  // map from edge vertices to their index in `edges` vector
+  std::unordered_map<std::pair<int, int>, int, PairHash> edge_indices;
+
+  // loop over all triangles
+  for (int t = 0; t < nt; t++) {
+    int* v = elements[t].vertices;
+
+    // compute edges to vertices map for fast computations
+    for (int e = 0; e < kNumEdges; e++) {
+      auto pair = std::pair(
+        std::min(v[edge[e][0]], v[edge[e][1]]),
+        std::max(v[edge[e][0]], v[edge[e][1]])
+      );
+
+      // if edge is already present in the vector only store its index
+      auto [it, inserted] = edge_indices.insert({pair, ne});
+
+      if (inserted) {
+        StencilFlap flap;
+        flap.vertices[0] = v[edge[e][0]];
+        flap.vertices[1] = v[edge[e][1]];
+        flap.vertices[2] = v[(edge[e][1]+1) % 3];
+        flap.vertices[3] = -1;
+        flaps.push_back(flap);
+        elements[t].edges[e] = ne++;
+      } else {
+        elements[t].edges[e] = it->second;
+        flaps[it->second].vertices[3] = v[(edge[e][1]+1) % 3];
+      }
+    }
+  }
+}
+
+// plugin constructor
+Shell::Shell(const mjModel* m, mjData* d, int instance, mjtNum nu, mjtNum E,
+             mjtNum damp, mjtNum thick, const std::vector<int>& face)
+    : damping(damp), thickness(thick) {
+  // count plugin bodies
+  nv = ne = 0;
+  for (int i = 1; i < m->nbody; i++) {
+    if (m->body_plugin[i] == instance) {
+      if (!nv++) {
+        i0 = i;
+      }
+    }
+  }
+
+  // generate triangles from the vertices
+  CreateStencils(face);
+
+  // material parameters
+  mjtNum mu = E / (2*(1+nu));
+
+  // loop over all triangles
+  for (int t = 0; t < nt; t++) {
+    int* v = elements[t].vertices;
+    for (int i = 0; i < kNumVerts; i++) {
+      if (m->body_plugin[i0+v[i]] != instance) {
+        mju_error("This body does not have the requested plugin instance");
+      }
+    }
+  }
+
+  // allocate array
+  position.assign(nv*3, 0);
+  bending.assign(ne*16, 0);
+
+  // store previous positions
+  mju_copy(position.data(), m->body_pos+3*i0, 3*nv);
+
+  // assemble bending Hessian
+  for (int e = 0; e < ne; e++)  {
+    int* v = flaps[e].vertices;
+    int vadj[3] = {v[1], v[0], v[3]};
+
+    if (v[3]== -1) {
+      // skip boundary edges
+      continue;
+    }
+
+    // cotangent operator from Wardetzky at al., "Discrete Quadratic Curvature
+    // Energies", https://cims.nyu.edu/gcl/papers/wardetzky2007dqb.pdf
+
+    mjtNum a01 = cot(m->body_pos+3*i0, v[0], v[1], v[2]);
+    mjtNum a02 = cot(m->body_pos+3*i0, v[0], v[3], v[1]);
+    mjtNum a03 = cot(m->body_pos+3*i0, v[1], v[2], v[0]);
+    mjtNum a04 = cot(m->body_pos+3*i0, v[1], v[0], v[3]);
+    mjtNum c[4] = {a03 + a04, a01 + a02, -(a01 + a03), -(a02 + a04)};
+    mjtNum volume = ComputeVolume(m->body_pos+3*i0, v) +
+                    ComputeVolume(m->body_pos+3*i0, vadj);
+
+    for (int v1 = 0; v1 < StencilFlap::kNumVerts; v1++) {
+      for (int v2 = 0; v2 < StencilFlap::kNumVerts; v2++) {
+        bending[16 * e + 4 * v1 + v2] +=
+            1.5 * c[v1] * c[v2] / volume * mu * pow(thickness, 3) / 12;
+      }
+    }
+  }
+}
+
+void Shell::Compute(const mjModel* m, mjData* d, int instance) {
+  mjtNum kD = damping / m->opt.timestep;
+
+  // compute bending contribution
+  mjtNum embedding;
+  for (int e = 0; e < ne; e++) {
+    int* v = flaps[e].vertices;
+    mjtNum force[12] = {0};
+    if (v[3] == -1) {
+      // skip boundary edges
+      continue;
+    }
+    for (int i = 0; i < StencilFlap::kNumVerts; i++) {
+      for (int j = 0; j < StencilFlap::kNumVerts; j++) {
+        for (int x = 0; x < 3; x++) {
+          embedding = d->xpos[3*(i0+v[j])+x]*(kD+1) - position[3*v[j]+x]*kD;
+          force[3*i+x] += bending[16*e+4*i+j] * embedding;
+        }
+      }
+    }
+
+    // update stored positions
+    mju_copy(position.data(), d->xpos+3*i0, 3*nv);
+
+    // insert into global force
+    for (int i = 0; i < StencilFlap::kNumVerts; i++) {
+      for (int x = 0; x < 3; x++) {
+        d->qfrc_passive[m->body_dofadr[i0]+3*v[i]+x] -= force[3*i+x];
+      }
+    }
+  }
+}
+
+
+
+void Shell::RegisterPlugin() {
+  mjpPlugin plugin;
+  mjp_defaultPlugin(&plugin);
+
+  plugin.name = "mujoco.elasticity.shell";
+  plugin.capabilityflags |= mjPLUGIN_PASSIVE;
+
+  const char* attributes[] = {"face", "young", "poisson", "damping",
+                              "thickness"};
+  plugin.nattribute = sizeof(attributes) / sizeof(attributes[0]);
+  plugin.attributes = attributes;
+  plugin.nstate = +[](const mjModel* m, int instance) { return 0; };
+
+  plugin.init = +[](const mjModel* m, mjData* d, int instance) {
+    auto elasticity_or_null = Shell::Create(m, d, instance);
+    if (!elasticity_or_null.has_value()) {
+      return -1;
+    }
+    d->plugin_data[instance] = reinterpret_cast<uintptr_t>(
+        new Shell(std::move(*elasticity_or_null)));
+    return 0;
+  };
+  plugin.destroy = +[](mjData* d, int instance) {
+    delete reinterpret_cast<Shell*>(d->plugin_data[instance]);
+    d->plugin_data[instance] = 0;
+  };
+  plugin.compute = +[](const mjModel* m, mjData* d, int instance, int type) {
+    auto* elasticity = reinterpret_cast<Shell*>(d->plugin_data[instance]);
+    elasticity->Compute(m, d, instance);
+  };
+
+  mjp_registerPlugin(&plugin);
+}
+
+}  // namespace mujoco::plugin::elasticity
diff --git a/plugin/elasticity/shell.h b/plugin/elasticity/shell.h
new file mode 100644
index 00000000..16dc66a5
--- /dev/null
+++ b/plugin/elasticity/shell.h
@@ -0,0 +1,79 @@
+// Copyright 2023 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MUJOCO_PLUGIN_ELASTICITY_SHELL_H_
+#define MUJOCO_PLUGIN_ELASTICITY_SHELL_H_
+
+#include <optional>
+#include <vector>
+
+#include <mujoco/mjdata.h>
+#include <mujoco/mjmodel.h>
+#include <mujoco/mjtnum.h>
+
+
+namespace mujoco::plugin::elasticity {
+
+struct Stencil2D {
+  static constexpr int kNumEdges = 3;
+  static constexpr int kNumVerts = 3;
+  int vertices[kNumVerts];
+  int edges[kNumEdges];
+};
+
+struct StencilFlap {
+  static constexpr int kNumVerts = 4;
+  int vertices[kNumVerts];
+};
+
+class Shell {
+ public:
+  // Returns a new Shell instance or nullopt on failure.
+  static std::optional<Shell> Create(const mjModel* m, mjData* d,
+                                     int instance);
+  Shell(Shell&&) = default;
+
+  Shell& operator=(Shell&& other) = default;
+
+  void Compute(const mjModel* m, mjData* d, int instance);
+
+  static void RegisterPlugin();
+
+  int i0;  // index of first body
+  int nc;  // number of quads in the grid
+  int nv;  // number of vertices (bodies) in the Shell
+  int nt;  // number of area elements (triangles)
+  int ne;  // number of edges in the Shell
+
+  // connectivity info for mapping tetrahedra to edges and vertices
+  std::vector<Stencil2D> elements;          // triangles              (nt x 6)
+  std::vector<StencilFlap> flaps;           // adjacent triangles     (ne x 4)
+
+  // precomputed quantities
+  std::vector<mjtNum> position;             // previous-step positions (nv x 3)
+  std::vector<mjtNum> bending;              // bending Hessian         (ne x 16)
+
+  mjtNum damping;
+  mjtNum thickness;
+
+ private:
+  Shell(const mjModel* m, mjData* d, int instance, mjtNum nu, mjtNum E,
+        mjtNum damp, mjtNum thick, const std::vector<int>& face);
+
+  void CreateStencils(const std::vector<int>& face);
+};
+
+}  // namespace mujoco::plugin::elasticity
+
+#endif  // MUJOCO_PLUGIN_ELASTICITY_SHELL_H_
diff --git a/src/user/user_composite.cc b/src/user/user_composite.cc
index b150f27b..2becbc02 100644
--- a/src/user/user_composite.cc
+++ b/src/user/user_composite.cc
@@ -14,6 +14,7 @@
 
 #include "user/user_composite.h"
 
+#include <algorithm>
 #include <cmath>
 #include <cstddef>
 #include <cstdio>
@@ -25,9 +26,9 @@
 
 #include <mujoco/mjmacro.h>
 #include <mujoco/mjmodel.h>
+#include <mujoco/mujoco.h>
 #include "cc/array_safety.h"
 #include "engine/engine_io.h"
-#include "engine/engine_macro.h"
 #include "engine/engine_util_blas.h"
 #include "engine/engine_util_errmem.h"
 #include "engine/engine_util_misc.h"
@@ -394,7 +395,7 @@ bool mjCComposite::MakeParticle(mjCModel* model, mjCBody* body, char* error, int
   std::vector<mjtNum> volume(uservert.size()/3);
   mjtNum t = 1;
   if (dim == 2 && plugin_instance) {
-    // do nothing for now (until new passive forces are supported)
+    t = stod(plugin_instance->config_attribs["thickness"], nullptr);
   }
   if (!userface.empty()) {
     mjXUtil::String2Vector(userface, face);
@@ -487,6 +488,49 @@ bool mjCComposite::MakeParticle(mjCModel* model, mjCBody* body, char* error, int
     }
   }
 
+  // add isometry constraints
+  if (dim==2) {
+    char txt0[100], txt1[100], txt2[100];
+    std::vector<std::pair<int, int>> edge;
+
+    // create edges
+    for (int i=0; i<face.size()/3; i++) {
+      for (int j=0; j<3; j++) {
+        int v0 = face[3*i+(j+0)%3]-1;
+        int v1 = face[3*i+(j+1)%3]-1;
+        edge.push_back(v0 < v1 ? std::pair(v0, v1) : std::pair(v1, v0));
+      }
+    }
+
+    std::sort(edge.begin(), edge.end());
+    auto last = std::unique(edge.begin(), edge.end());
+    edge.erase(last, edge.end());
+
+    // create constraints
+    for (int i=0; i<edge.size(); i++) {
+      int v0 = edge[i].first;
+      int v1 = edge[i].second;
+
+      mju::sprintf_arr(txt0, "%sT%d_%d", prefix.c_str(), v0, v1);
+      mju::sprintf_arr(txt1, "%sS%d", prefix.c_str(), v0);
+      mju::sprintf_arr(txt2, "%sS%d", prefix.c_str(), v1);
+
+      // create tendon
+      mjCTendon* ten = model->AddTendon(def + mjCOMPKIND_TENDON);
+      ten->def = model->defaults[0];
+      ten->name = txt0;
+      ten->group = 4;
+      ten->WrapSite(txt1);
+      ten->WrapSite(txt2);
+
+      // add equality constraint
+      mjCEquality* eq = model->AddEquality(def + mjCOMPKIND_TENDON);
+      eq->def = model->defaults[0];
+      eq->type = mjEQ_TENDON;
+      eq->name1 = ten->name;
+    }
+  }
+
   if (skin) {
     MakeSkin3(model);
   }
diff --git a/test/engine/engine_plugin_test.cc b/test/engine/engine_plugin_test.cc
index abc69e82..8e1bc9e0 100644
--- a/test/engine/engine_plugin_test.cc
+++ b/test/engine/engine_plugin_test.cc
@@ -32,7 +32,7 @@ namespace {
 using ::testing::HasSubstr;
 using ::testing::NotNull;
 
-constexpr int kNumTruePlugins = 9;
+constexpr int kNumTruePlugins = 10;
 constexpr int kNumFakePlugins = 30;
 constexpr int kNumTestPlugins = 3;
 
diff --git a/test/plugin/elasticity/elasticity_test.cc b/test/plugin/elasticity/elasticity_test.cc
index d2e36025..614026f4 100644
--- a/test/plugin/elasticity/elasticity_test.cc
+++ b/test/plugin/elasticity/elasticity_test.cc
@@ -14,23 +14,77 @@
 
 // Tests for plugin-related functionalities.
 
-#include <array>
-#include <cstdint>
-#include <cstring>
-#include <sstream>
+#include <cmath>
+#include <limits>
 #include <vector>
 
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 #include <mujoco/mujoco.h>
 #include "test/fixture.h"
+#include "plugin/elasticity/shell.h"
 #include "plugin/elasticity/solid.h"
 
 namespace mujoco {
 namespace {
 
+
+// -------------------------------- shell -----------------------------------
+TEST_F(PluginTest, ElasticEnergyShell) {
+  static constexpr char cantilever_xml[] = R"(
+  <mujoco>
+  <extension>
+    <plugin plugin="mujoco.elasticity.shell"/>
+  </extension>
+
+  <worldbody>
+    <composite type="particle" count="8 8 1" spacing="1">
+      <geom size=".025" group="4"/>
+      <plugin plugin="mujoco.elasticity.shell">
+        <config key="poisson" value="0"/>
+        <config key="young" value="2"/>
+        <config key="thickness" value="1"/>
+      </plugin>
+    </composite>
+  </worldbody>
+  </mujoco>
+  )";
+
+  char error[1024] = {0};
+  mjModel* m = LoadModelFromString(cantilever_xml, error, sizeof(error));
+  ASSERT_THAT(m, testing::NotNull()) << error;
+  mjData* d = mj_makeData(m);
+  auto* shell = reinterpret_cast<plugin::elasticity::Shell*>(d->plugin_data[0]);
+
+  // check that a plane is in the kernel of the energy
+  for (mjtNum scale = 1; scale < 4; scale++) {
+    for (int e = 0; e < shell->ne; e++) {
+      int* v = shell->flaps[e].vertices;
+      if (v[3]== -1) {
+        continue;
+      }
+      mjtNum energy = 0;
+      mjtNum volume = 1./2.;
+      for (int i = 0; i < 4; i++) {
+        for (int j = 0; j < 4; j++) {
+          for (int x = 0; x < 3; x++) {
+            mjtNum elongation1 = scale * shell->position[3*v[i]+x];
+            mjtNum elongation2 = scale * shell->position[3*v[j]+x];
+            energy += shell->bending[16*e+4*i+j] * elongation1 * elongation2;
+          }
+        }
+      }
+      EXPECT_NEAR(
+        4*energy/volume, 0, std::numeric_limits<float>::epsilon());
+    }
+  }
+
+  mj_deleteData(d);
+  mj_deleteModel(m);
+}
+
 // -------------------------------- solid -----------------------------------
-TEST_F(PluginTest, ElasticEnergy) {
+TEST_F(PluginTest, ElasticEnergySolid) {
   static constexpr char cantilever_xml[] = R"(
   <mujoco>
   <extension>