Marrow: GPU Tetrahedral Soft Body for Blender

Blender's soft body modifier is a spring lattice stretched over your surface. It has no volume, so a squashed sphere stays squashed and a pressed arm goes flat instead of bulging. Marrow fills the mesh with a tetrahedral cage and solves real material through it on the GPU - so the flesh displaces, bulges and comes back, and a live frame still costs 1 to 2 ms.

You have a creature, a limb, a belly or a tentacle, and you need it to move like something with material inside it.

Blender ships XPBD for hair, cloth and particles. It ships nothing volumetric. The legacy SOFT_BODY modifier is a spring lattice on the surface with no volume term at all, so it cannot bulge, cannot preserve volume under a press, and reads as a wobbling shell rather than as flesh.

Marrow fills the mesh with a tetrahedral cage, solves a stable neo-Hookean XPBD system through it in GLSL compute shaders, and deforms your render mesh by barycentric interpolation from the cage. Your mesh is never rebuilt - the cage is a separate hidden object, and De-tetrahedralize hands the modelled mesh back bit for bit.

Move a slider, return to the start frame, and the sim restarts with the new value without freeing or rebaking the cache. Select twenty muscles and Tetrahedralize once - the whole selection is caged under a single progress bar, and Esc stops it wherever it got to and keeps the cages already built.

Drag into a wall and it squashes, because a collider still outranks your hand. Drag on empty space and the view orbits instead, so a drag session never has to be cancelled just to look at the pile from another angle. This is the fastest way to find out what a material setting actually feels like.

Things to know before purchasing

Please read this section. Every limitation is listed here on purpose, and a refund request based on a feature that is not listed above cannot be accepted.

Blender 5.2 or newer. It will not run on 4.x.

You need a GPU that runs compute shaders. There is no CPU fallback.

Contact is node against node. No edge-edge or node-triangle contact, and neither self-collision nor body-to-body scales past roughly 20,000 surface nodes. Collision against a collider is a distance field and has no such limit.

A deforming collider is baked once. Transform animation is free; deformation is not.

Friction does not ride a moving collider. Sticky is how a moving collider carries material.

A body must not start already overlapping a sticky collider. Measured on a sphere half-buried in a sticky box, 219 of 461 nodes seized on the first frame and the render mesh shredded.

No plasticity. A dent springs back rather than staying dented.

Quasistatic wants a soft material. Past roughly Stiffness 1e4 the solve is under-converged at any Iterations count.

A live cache lives only in memory. Bakes are written beside the .blend and reload with it.

Glue is one way and one frame coarse.

Fiber curves and Shell are baked at Tetrahedralize. A bevelled or cyclic curve bakes no fibers at all.

Body-to-body contact is a few bodies, not a crowd. N bodies make N² pairs.

FAQ

Does it change my mesh?No. The cage is a separate hidden object and your render mesh is deformed by interpolation from it. De-tetrahedralize returns the mesh bit-identical.

Does it work with my rig?Yes - that is what Attachment is for. Tetrahedralizing an already-rigged model turns it on for you.

Cycles or EEVEE?Both, and neither. Marrow deforms geometry; it does not shade anything.

Do I need to install anything else?No. Pure Python against Blender's bundled interpreter - no compiled binary, no dependency, no pip install.

Will my bake survive closing the file?Yes, in a blendcache_ folder beside the .blend, the same convention Blender's own point caches use.

How is this different from the Soft Body modifier?The modifier is a spring lattice on the surface with no volume term. Marrow solves a neo-Hookean material through a cage that fills the interior.

Can I use it commercially?Yes.