> This page is for version Release 2.1.
> For other versions, use one of these documentation indexes:
> - Release 3.0 (default): https://docs.nvidia.com/isaaclab/3.0/llms.txt
> - Release 2.3: https://docs.nvidia.com/isaaclab/2.3/llms.txt
> - Release 2.2: https://docs.nvidia.com/isaaclab/2.2/llms.txt
> - Release 2.1: https://docs.nvidia.com/isaaclab/2.1/llms.txt

> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/isaaclab/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/isaaclab/_mcp/server.

# Interacting with a deformable object

While deformable objects sometimes refer to a broader class of objects, such as cloths, fluids and soft bodies,
in PhysX, deformable objects syntactically correspond to soft bodies. Unlike rigid objects, soft bodies can deform
under external forces and collisions.

Soft bodies are simulated using Finite Element Method (FEM) in PhysX. The soft body comprises of two tetrahedral
meshes -- a simulation mesh and a collision mesh. The simulation mesh is used to simulate the deformations of
the soft body, while the collision mesh is used to detect collisions with other objects in the scene.
For more details, please check the [PhysX documentation](https://nvidia-omniverse.github.io/PhysX/physx/5.4.1/docs/SoftBodies.html).

This tutorial shows how to interact with a deformable object in the simulation. We will spawn a
set of soft cubes and see how to set their nodal positions and velocities, along with apply kinematic
commands to the mesh nodes to move the soft body.

## The Code

The tutorial corresponds to the `run_deformable_object.py` script in the `scripts/tutorials/01_assets` directory.

```python
# Copyright (c) 2022-2025, The Isaac Lab Project Developers.
# All rights reserved.
#
# SPDX-License-Identifier: BSD-3-Clause

"""
This script demonstrates how to work with the deformable object and interact with it.

~~~bash
# Usage
./isaaclab.sh -p scripts/tutorials/01_assets/run_deformable_object.py
~~~

"""

"""Launch Isaac Sim Simulator first."""

import argparse

from isaaclab.app import AppLauncher

# add argparse arguments
parser = argparse.ArgumentParser(description="Tutorial on interacting with a deformable object.")
# append AppLauncher cli args
AppLauncher.add_app_launcher_args(parser)
# parse the arguments
args_cli = parser.parse_args()

# launch omniverse app
app_launcher = AppLauncher(args_cli)
simulation_app = app_launcher.app

"""Rest everything follows."""

import torch

import isaacsim.core.utils.prims as prim_utils

import isaaclab.sim as sim_utils
import isaaclab.utils.math as math_utils
from isaaclab.assets import DeformableObject, DeformableObjectCfg
from isaaclab.sim import SimulationContext

def design_scene():
    """Designs the scene."""
    # Ground-plane
    cfg = sim_utils.GroundPlaneCfg()
    cfg.func("/World/defaultGroundPlane", cfg)
    # Lights
    cfg = sim_utils.DomeLightCfg(intensity=2000.0, color=(0.8, 0.8, 0.8))
    cfg.func("/World/Light", cfg)

    # Create separate groups called "Origin1", "Origin2", "Origin3"
    # Each group will have a robot in it
    origins = [[0.25, 0.25, 0.0], [-0.25, 0.25, 0.0], [0.25, -0.25, 0.0], [-0.25, -0.25, 0.0]]
    for i, origin in enumerate(origins):
        prim_utils.create_prim(f"/World/Origin{i}", "Xform", translation=origin)

    # Deformable Object
    cfg = DeformableObjectCfg(
        prim_path="/World/Origin.*/Cube",
        spawn=sim_utils.MeshCuboidCfg(
            size=(0.2, 0.2, 0.2),
            deformable_props=sim_utils.DeformableBodyPropertiesCfg(rest_offset=0.0, contact_offset=0.001),
            visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.5, 0.1, 0.0)),
            physics_material=sim_utils.DeformableBodyMaterialCfg(poissons_ratio=0.4, youngs_modulus=1e5),
        ),
        init_state=DeformableObjectCfg.InitialStateCfg(pos=(0.0, 0.0, 1.0)),
        debug_vis=True,
    )
    cube_object = DeformableObject(cfg=cfg)

    # return the scene information
    scene_entities = {"cube_object": cube_object}
    return scene_entities, origins

def run_simulator(sim: sim_utils.SimulationContext, entities: dict[str, DeformableObject], origins: torch.Tensor):
    """Runs the simulation loop."""
    # Extract scene entities
    # note: we only do this here for readability. In general, it is better to access the entities directly from
    #   the dictionary. This dictionary is replaced by the InteractiveScene class in the next tutorial.
    cube_object = entities["cube_object"]
    # Define simulation stepping
    sim_dt = sim.get_physics_dt()
    sim_time = 0.0
    count = 0

    # Nodal kinematic targets of the deformable bodies
    nodal_kinematic_target = cube_object.data.nodal_kinematic_target.clone()

    # Simulate physics
    while simulation_app.is_running():
        # reset
        if count % 250 == 0:
            # reset counters
            sim_time = 0.0
            count = 0

            # reset the nodal state of the object
            nodal_state = cube_object.data.default_nodal_state_w.clone()
            # apply random pose to the object
            pos_w = torch.rand(cube_object.num_instances, 3, device=sim.device) * 0.1 + origins
            quat_w = math_utils.random_orientation(cube_object.num_instances, device=sim.device)
            nodal_state[..., :3] = cube_object.transform_nodal_pos(nodal_state[..., :3], pos_w, quat_w)

            # write nodal state to simulation
            cube_object.write_nodal_state_to_sim(nodal_state)

            # Write the nodal state to the kinematic target and free all vertices
            nodal_kinematic_target[..., :3] = nodal_state[..., :3]
            nodal_kinematic_target[..., 3] = 1.0
            cube_object.write_nodal_kinematic_target_to_sim(nodal_kinematic_target)

            # reset buffers
            cube_object.reset()

            print("----------------------------------------")
            print("[INFO]: Resetting object state...")

        # update the kinematic target for cubes at index 0 and 3
        # we slightly move the cube in the z-direction by picking the vertex at index 0
        nodal_kinematic_target[[0, 3], 0, 2] += 0.001
        # set vertex at index 0 to be kinematically constrained
        # 0: constrained, 1: free
        nodal_kinematic_target[[0, 3], 0, 3] = 0.0
        # write kinematic target to simulation
        cube_object.write_nodal_kinematic_target_to_sim(nodal_kinematic_target)

        # write internal data to simulation
        cube_object.write_data_to_sim()
        # perform step
        sim.step()
        # update sim-time
        sim_time += sim_dt
        count += 1
        # update buffers
        cube_object.update(sim_dt)
        # print the root position
        if count % 50 == 0:
            print(f"Root position (in world): {cube_object.data.root_pos_w[:, :3]}")

def main():
    """Main function."""
    # Load kit helper
    sim_cfg = sim_utils.SimulationCfg(device=args_cli.device)
    sim = SimulationContext(sim_cfg)
    # Set main camera
    sim.set_camera_view(eye=[3.0, 0.0, 1.0], target=[0.0, 0.0, 0.5])
    # Design scene
    scene_entities, scene_origins = design_scene()
    scene_origins = torch.tensor(scene_origins, device=sim.device)
    # Play the simulator
    sim.reset()
    # Now we are ready!
    print("[INFO]: Setup complete...")
    # Run the simulator
    run_simulator(sim, scene_entities, scene_origins)

if __name__ == "__main__":
    # run the main function
    main()
    # close sim app
    simulation_app.close()
```

## The Code Explained

### Designing the scene

Similar to the [Interacting with a rigid object](/source/tutorials/01_assets/run_rigid_object) tutorial, we populate the scene with a ground plane
and a light source. In addition, we add a deformable object to the scene using the `assets.DeformableObject`
class. This class is responsible for spawning the prims at the input path and initializes their corresponding
deformable body physics handles.

In this tutorial, we create a cubical soft object using the spawn configuration similar to the deformable cube
in the [Spawn Objects](/source/tutorials/00_sim/spawn_prims) tutorial. The only difference is that now we wrap
the spawning configuration into the `assets.DeformableObjectCfg` class. This class contains information about
the asset's spawning strategy and default initial state. When this class is passed to
the `assets.DeformableObject` class, it spawns the object and initializes the corresponding physics handles
when the simulation is played.

> **Note**
>
> The deformable object is only supported in GPU simulation and requires a mesh object to be spawned with the
> deformable body physics properties on it.

As seen in the rigid body tutorial, we can spawn the deformable object into the scene in a similar fashion by creating
an instance of the `assets.DeformableObject` class by passing the configuration object to its constructor.

```python
# Create separate groups called "Origin1", "Origin2", "Origin3"
# Each group will have a robot in it
origins = [[0.25, 0.25, 0.0], [-0.25, 0.25, 0.0], [0.25, -0.25, 0.0], [-0.25, -0.25, 0.0]]
for i, origin in enumerate(origins):
    prim_utils.create_prim(f"/World/Origin{i}", "Xform", translation=origin)

# Deformable Object
cfg = DeformableObjectCfg(
    prim_path="/World/Origin.*/Cube",
    spawn=sim_utils.MeshCuboidCfg(
        size=(0.2, 0.2, 0.2),
        deformable_props=sim_utils.DeformableBodyPropertiesCfg(rest_offset=0.0, contact_offset=0.001),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.5, 0.1, 0.0)),
        physics_material=sim_utils.DeformableBodyMaterialCfg(poissons_ratio=0.4, youngs_modulus=1e5),
    ),
    init_state=DeformableObjectCfg.InitialStateCfg(pos=(0.0, 0.0, 1.0)),
    debug_vis=True,
)
cube_object = DeformableObject(cfg=cfg)
```

### Running the simulation loop

Continuing from the rigid body tutorial, we reset the simulation at regular intervals, apply kinematic commands
to the deformable body, step the simulation, and update the deformable object's internal buffers.

#### Resetting the simulation state

Unlike rigid bodies and articulations, deformable objects have a different state representation. The state of a
deformable object is defined by the nodal positions and velocities of the mesh. The nodal positions and velocities
are defined in the **simulation world frame** and are stored in the `assets.DeformableObject.data` attribute.

We use the `assets.DeformableObject.data.default_nodal_state_w` attribute to get the default nodal state of the
spawned object prims. This default state can be configured from the `assets.DeformableObjectCfg.init_state`
attribute, which we left as identity in this tutorial.

> **Warning**
>
> The initial state in the configuration `assets.DeformableObjectCfg` specifies the pose
> of the deformable object at the time of spawning. Based on this initial state, the default nodal state is
> obtained when the simulation is played for the first time.

We apply transformations to the nodal positions to randomize the initial state of the deformable object.

```python
# reset the nodal state of the object
nodal_state = cube_object.data.default_nodal_state_w.clone()
# apply random pose to the object
pos_w = torch.rand(cube_object.num_instances, 3, device=sim.device) * 0.1 + origins
quat_w = math_utils.random_orientation(cube_object.num_instances, device=sim.device)
nodal_state[..., :3] = cube_object.transform_nodal_pos(nodal_state[..., :3], pos_w, quat_w)
```

To reset the deformable object, we first set the nodal state by calling the `assets.DeformableObject.write_nodal_state_to_sim`
method. This method writes the nodal state of the deformable object prim into the simulation buffer.
Additionally, we free all the kinematic targets set for the nodes in the previous simulation step by calling
the `assets.DeformableObject.write_nodal_kinematic_target_to_sim` method. We explain the
kinematic targets in the next section.

Finally, we call the `assets.DeformableObject.reset` method to reset any internal buffers and caches.

```python
# write nodal state to simulation
cube_object.write_nodal_state_to_sim(nodal_state)

# Write the nodal state to the kinematic target and free all vertices
nodal_kinematic_target[..., :3] = nodal_state[..., :3]
nodal_kinematic_target[..., 3] = 1.0
cube_object.write_nodal_kinematic_target_to_sim(nodal_kinematic_target)

# reset buffers
cube_object.reset()
```

#### Stepping the simulation

Deformable bodies support user-driven kinematic control where a user can specify position targets for some of
the mesh nodes while the rest of the nodes are simulated using the FEM solver. This [partial kinematic](https://nvidia-omniverse.github.io/PhysX/physx/5.4.1/docs/SoftBodies.html#kinematic-soft-bodies) control
is useful for applications where the user wants to interact with the deformable object in a controlled manner.

In this tutorial, we apply kinematic commands to two out of the four cubes in the scene. We set the position
targets for the node at index 0 (bottom-left corner) to move the cube along the z-axis.

At every step, we increment the kinematic position target for the node by a small value. Additionally,
we set the flag to indicate that the target is a kinematic target for that node in the simulation buffer.
These are set into the simulation buffer by calling the `assets.DeformableObject.write_nodal_kinematic_target_to_sim`
method.

```python
# update the kinematic target for cubes at index 0 and 3
# we slightly move the cube in the z-direction by picking the vertex at index 0
nodal_kinematic_target[[0, 3], 0, 2] += 0.001
# set vertex at index 0 to be kinematically constrained
# 0: constrained, 1: free
nodal_kinematic_target[[0, 3], 0, 3] = 0.0
# write kinematic target to simulation
cube_object.write_nodal_kinematic_target_to_sim(nodal_kinematic_target)
```

Similar to the rigid object and articulation, we perform the `assets.DeformableObject.write_data_to_sim` method
before stepping the simulation. For deformable objects, this method does not apply any external forces to the object.
However, we keep this method for completeness and future extensions.

```python
# write internal data to simulation
cube_object.write_data_to_sim()
```

#### Updating the state

After stepping the simulation, we update the internal buffers of the deformable object prims to reflect their new state
inside the `assets.DeformableObject.data` attribute. This is done using the `assets.DeformableObject.update` method.

At a fixed interval, we print the root position of the deformable object to the terminal. As mentioned
earlier, there is no concept of a root state for deformable objects. However, we compute the root position as
the average position of all the nodes in the mesh.

```python
# update buffers
cube_object.update(sim_dt)
# print the root position
if count % 50 == 0:
    print(f"Root position (in world): {cube_object.data.root_pos_w[:, :3]}")
```

## The Code Execution

Now that we have gone through the code, let's run the script and see the result:

```bash
./isaaclab.sh -p scripts/tutorials/01_assets/run_deformable_object.py
```

This should open a stage with a ground plane, lights, and several green cubes. Two of the four cubes must be dropping
from a height and settling on to the ground. Meanwhile the other two cubes must be moving along the z-axis. You
should see a marker showing the kinematic target position for the nodes at the bottom-left corner of the cubes.
To stop the simulation, you can either close the window, or press `Ctrl+C` in the terminal

![result of run\_deformable\_object.py](/isaaclab/_fern-img/efe61c1fbb7bd6b6e437613379986a7ce26e8790ab330ab545f0a8f06a9f905e.webp)

This tutorial showed how to spawn deformable objects and wrap them in a `DeformableObject` class to initialize their
physics handles which allows setting and obtaining their state. We also saw how to apply kinematic commands to the
deformable object to move the mesh nodes in a controlled manner. In the next tutorial, we will see how to create
a scene using the `InteractiveScene` class.