🧪 Material Parameters¶

Per-object material parameters. Set via object.param.set(key, value) on a frontend.Object. The solver exposes three element types, each with its own defaults:

tri: triangle shells (cloth).
tet: tetrahedral solids.
rod: rod / edge elements.

(not applicable) in a default column means the given element type does not expose that parameter.

model¶

Key	`model`
Default (tri)	`'baraff-witkin'`
Default (tet)	`'arap'`
Default (rod)	`'arap'`
Label	Deformation Model
Description	Elastic constitutive model used to evaluate stretch energy. Valid choices are ‘arap’, ‘stvk’, ‘baraff-witkin’ (shells only), and ‘snhk’ (stable neo-Hookean). Rods are always solved with ARAP internally.

density¶

Key	`density`
Default (tri)	`1.0`
Default (tet)	`1000.0`
Default (rod)	`1.0`
Label	Density
Description	Rest-state mass density. Units depend on element type: kg/m^3 for ‘tet’ (volumetric), kg/m^2 for ‘tri’ (areal), and kg/m for ‘rod’ (linear). Must be positive.

young-mod¶

Key	`young-mod`
Default (tri)	`1000.0`
Default (tet)	`500.0`
Default (rod)	`10000.0`
Label	Young’s Modulus
Description	Stiffness coefficient fed into the constitutive model, pre-normalized by density (units of Pa/rho). This decouples mass from stiffness, so doubling density alone leaves the motion unchanged. Must be positive.

poiss-rat¶

Key	`poiss-rat`
Default (tri)	`0.35`
Default (tet)	`0.35`
Default (rod)	`0.35`
Label	Poisson’s Ratio
Description	Poisson’s ratio used together with Young’s modulus to derive the Lame parameters. Valid range is (0, 0.5); values near 0.5 produce near-incompressible behavior. Used by ‘tri’ and ‘tet’ elements only.

bend¶

Key	`bend`
Default (tri)	`10.0`
Default (tet)	`1.0`
Default (rod)	`0.0`
Label	Bending Stiffness
Description	Dimensionless bending stiffness for shell hinges (between adjacent ‘tri’ faces) and for rod-joint bending at interior rod vertices. Must be non-negative. Not used by ‘tet’ elements.

shrink-x¶

Key	`shrink-x`
Default (tri)	`1.0`
Default (tet)	`1.0`
Default (rod)	`1.0`
Label	Shrink X
Description	Anisotropic rest-shape scale along the UV X (warp) direction for ‘tri’ shells. Values below 1.0 pre-shrink the cloth, above 1.0 pre-stretch it. Must be positive. Cannot be combined with a non-zero strain limit on the same face.

shrink-y¶

Key	`shrink-y`
Default (tri)	`1.0`
Default (tet)	`1.0`
Default (rod)	`1.0`
Label	Shrink Y
Description	Anisotropic rest-shape scale along the UV Y (weft) direction for ‘tri’ shells. Values below 1.0 pre-shrink the cloth, above 1.0 pre-stretch it. Must be positive. Cannot be combined with a non-zero strain limit on the same face.

shrink¶

Key	`shrink`
Default (tri)	`1.0`
Default (tet)	`1.0`
Default (rod)	`1.0`
Label	Shrink
Description	Isotropic rest-shape scale for ‘tet’ solids. Values below 1.0 pre-contract the solid so it pulls toward a smaller target, above 1.0 pre-inflate it. Must be positive. Ignored by ‘tri’ and ‘rod’ elements.

contact-gap¶

Key	`contact-gap`
Default (tri)	`0.001`
Default (tet)	`0.001`
Default (rod)	`0.001`
Label	Contact Gap
Description	Barrier activation distance for contact detection, in scene units. At each pair the solver uses the mean of the two participants’ gaps as the threshold. Must be positive.

contact-offset¶

Key	`contact-offset`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.001`
Label	Contact Offset
Description	Extra per-element padding added on top of the contact gap (scene units). At each pair the two participants’ offsets are summed, acting like a skin thickness that guarantees minimum clearance. Must be non-negative.

strain-limit¶

Key	`strain-limit`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Strain Limit
Description	Upper bound on per-element tensile strain (dimensionless, e.g. 0.05 = 5% stretch). 0.0 disables strain limiting. Supported on ‘tri’ and ‘rod’ elements only, and incompatible with non-unit shrink-x/shrink-y on the same face.

friction¶

Key	`friction`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Friction Coefficient
Description	Coulomb friction coefficient at contacts (dimensionless). When two elements touch, the solver uses the minimum of the two participants’ coefficients, so the more slippery side wins. Must be non-negative.

length-factor¶

Key	`length-factor`
Default (tri)	`1.0`
Default (tet)	`1.0`
Default (rod)	`1.0`
Label	Rod Rest-Length Factor
Description	Multiplier applied to each rod edge’s rest length (dimensionless). Values below 1.0 pre-tension the rod, above 1.0 pre-compress it. Must be positive. Used by ‘rod’ elements only.

pressure¶

Key	`pressure`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Inflation Pressure
Description	Per-face inflation pressure pushing ‘tri’ shells outward along the face normal. Must be non-negative; 0.0 disables inflation. Ignored by ‘tet’ and ‘rod’ elements.

plasticity¶

Key	`plasticity`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	(not applicable)
Label	Plasticity Rate
Description	Rate constant (per second) for stretch plasticity, driving the rest shape toward the current deformation via alpha = 1 - exp(-rate * dt). 0.0 disables plasticity; higher values creep faster. Must be non-negative.

plasticity-threshold¶

Key	`plasticity-threshold`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	(not applicable)
Label	Plasticity Threshold
Description	Dead zone (dimensionless) around unit principal stretch S=1. Plasticity only activates on a singular value k when \|S_k - 1\| exceeds this threshold. 0.0 means any deviation triggers creep.

bend-plasticity¶

Key	`bend-plasticity`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Bend Plasticity Rate
Description	Rate constant (per second) for bending plasticity that drifts the rest angle of shell hinges and interior rod joints toward the current angle. 0.0 disables. Applies to ‘tri’ and ‘rod’; kept on ‘tet’ only as a placeholder and ignored by the solver.

bend-plasticity-threshold¶

Key	`bend-plasticity-threshold`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Bend Plasticity Threshold
Description	Angular dead zone (radians) around the rest angle. Bend plasticity only activates when \|theta - theta_rest\| exceeds this threshold. 0.0 means any angular deviation triggers creep.

bend-rest-from-geometry¶

Key	`bend-rest-from-geometry`
Default (tri)	`0.0`
Default (tet)	`0.0`
Default (rod)	`0.0`
Label	Bend Rest From Initial Geometry
Description	If non-zero, initialize each hinge or rod-joint rest angle from the initial pose instead of the default (flat for shells, straight for rods). Treated as a boolean flag.