Houdini 17.5 Shelf tools Vellum tab

Vellum Strut Softbody shelf tool

Configures Vellum strut softbody from geometry and adds to current Vellum simulation.

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This tool lets you pick a piece of geometry and configure it as Vellum strut softbody. It will then be added to the active simulation and merged with any other existing Vellum objects.

A strut softbody consists of two types of constraints. A cloth outer shell preserves the outer shape of the geometry and handles collisions. A collection of random struts are formed between opposite interior points to create a rough form of volume preservation. This is similar to connecting opposing points with toothpicks; so it can result in unusual results as it is not a true FEM solve.

Using Vellum Strut Softbody

  1. Select the geometry object to configure as Vellum strut softbody.

  2. Click the Vellum Strut Softbody tool on the Vellum tab.


There is a Surface Collider tool on the Vellum shelf that you can use for objects that will be colliding with your softbody. It is essentially the same as the Deforming Object shelf tool on the Collisions tab, as they are both designed for deforming objects. However the Surface Collider does not try to generate a VDB collision object, which is less expensive.

For specific parameter information, see the Vellum Constraints and Vellum Solver help.

Working with Strut Softbody

By default the Stretch Stiffness is very low on the Vellum Constraints node to make it more squishy. To make it less squishy you can increase this value.


If you make it too stiff you will see artifacts caused by the internal struts.

There are a few parameters in the Strut Search section that let you control how the struts are created. Typically the default values are sufficient, but you can change them to customize your softbody. For example, you can turn on Invert Normals which reverses the object’s normals. This is useful if the geometry has reversed normals, so that the struts can be properly created on the inside instead of the outside of the object.

Strut Softbody vs Tetrahedral Softbody

The Vellum Strut Softbody tool uses a collection of random struts that are formed between opposite interior points to create a rough form of volume preservation. This is similar to connecting opposing points with toothpicks to hold it apart, which in some poking artifacts. It also uses the original geometry to do the simulation.

The Vellum Tetrahedral Softbody tool will polyreduce, remesh to create a low-res proxy, and tetrahedralize the input geometry before simulation. Once the tetrahedral mesh is created, distance constraints are created along each edge to act as springs to maintain the general shape of the object and volume constraints are created to maintain the volume of each tetrahedron preventing the tets from collapsing in on themselves. Once the simulation is done, a Point Deform is used to automatically capture and deform the geometry.


You can also put down a Vellum Configure Tetrahedral Softbody using the TAB menu. However, this will only create a Solid Conform node, which tetrahedralizes your geometry. It will not simplify and remesh your geometry like the shelf tool does. It is important to note if you don’t polyreduce and remesh your geometry before tetrahedralizing it, not only will it be slower but it will likely also have widely varying tetrahedral sizes which could make it difficult to get the desired stiffness. This approach is for advance users.

Vellum tab