Materials

Each Atom material node outputs a Material that you connect to the Atom Solver. Every material has a Preset menu with SI values, and Custom keeps your own edits. Values are in real units.

Material	Model	Use it for
Sand	Drucker-Prager frictional plasticity	sand, soil, gravel
Elastic	Neo-Hookean hyperelastic, with optional tearing	rubber, jelly
Snow	Elastoplastic with fracture	snow that packs, then breaks
Mud & Clay	Yield-stress flow	mud that holds shape, then flows
Fluid	Weakly-compressible viscous liquid	slime, honey, oil
Lava	Thermo-viscous	lava that cools and crusts
Metal	Plasticity with hardening and failure	bending and tearing metal
Concrete	Brittle fracture	cracking and crumbling

Stiff materials (snow, stiff elastic, lava, metal, concrete) need more substeps to stay stable and cost more per frame. See Time and stability.

Sand

Setting	Default	What it does
Friction Angle	33°	Internal friction. It sets the angle of repose a pile settles at.
Cohesion (Pa)	0	Tensile strength between grains. 0 is dry sand, about 1 kPa is damp sand, a few kPa is soil.
Friction Hardening	off	Friction starts 10 degrees lower and rises as the material is worked (soil, compacting sand).
Young’s Modulus (Pa)	200,000	Grain-skeleton stiffness. Higher is closer to real sand and costs substeps.
Poisson Ratio	0.3	Resistance to volume change. 0.45 is nearly incompressible.
Density (kg/m³)	1600	Dry sand is about 1600, wet about 1900.

Elastic

Setting	Default	What it does
Young’s Modulus (Pa)	15,000	Stiffness. Gelatin is 5 to 50 kPa, rubber about 1 MPa.
Poisson Ratio	0.35	0.49 is nearly incompressible.
Damping (Pa·s)	40	How fast a wobble dies out. 0 rings until contacts stop it.
Critical Stretch	0	Stretch at which the material tears. 0.5 is 50% elongation. 0 never tears.
Density (kg/m³)	1050	Gelatin about 1050, rubber about 1100.

Snow

Setting	Default	What it does
Young’s Modulus (Pa)	140,000	Stiffness.
Poisson Ratio	0.2	Resistance to volume change.
Critical Compression	0.025	Compression past which snow packs down for good.
Critical Stretch	0.0075	Stretch past which snow breaks. Smaller is more brittle and chunkier.
Hardening	10	How much packing stiffens the snow.
Heat Conductivity	12	How fast heat reaches the snow, in 1e-4 m²/s.
Density (kg/m³)	400	Fresh snow about 100, packed about 400.

Mud and clay

Setting	Default	What it does
Kind	Mud	Flowing mud, or clay that stiffens when kneaded.
Yield Stress (Pa)	200	Shear stress below which it holds its shape. Mud is 50 to 500, clay 1 to 10 kPa.
Consistency (Pa·sⁿ)	20	Thickness once it flows.
Flow Index (n)	0.6	Below 1 is shear-thinning, 1 is a Bingham plastic, above 1 is shear-thickening.
Young’s Modulus (Pa)	50,000	Elastic stiffness below the yield stress.
Density (kg/m³)	1800	Wet mud is about 1800.

Fluid

Setting	Default	What it does
Viscosity (Pa·s)	0.001	Dynamic viscosity. Water is 0.001, oil about 0.1, honey about 10, slime a few.
Sound Speed (m/s)	12	Lower is more compressible. Higher is stiffer and costs substeps.
Surface Tension (N/m)	0	Rounds droplets. 0 is off.
Density (kg/m³)	1000	Water is 1000, honey about 1400.

Lava

Setting	Default	What it does
Hot Viscosity (Pa·s)	50	Viscosity of the molten lava. Basalt is 10 to 100.
Cold Viscosity (Pa·s)	300	Viscosity once cooled. High values cost substeps.
Crust Modulus (Pa)	200,000	Young’s modulus of the cooled crust.
Cooling Rate (/s)	0.25	How fast it loses heat. 0 never cools.
Heat Conduction	12	Thermal diffusivity, in 1e-4 m²/s.
Surface Tension	0.2	Pulls the lava into rounded blobs. 0 turns it off.
Density (kg/m³)	2600	Molten basalt.

Metal

Setting	Default	What it does
Young’s Modulus (Pa)	8,000,000	Scaled far below real steel (2e11 Pa) to keep the substep count practical.
Yield Stress (Pa)	40,000	Von Mises stress where the metal starts to bend and stay bent.
Hardening (Pa)	200,000	Yield stress gained per unit plastic strain.
Failure Strain	0.6	Plastic strain at which the metal tears. 0 never tears.
Density (kg/m³)	7800	Steel.

Concrete

Setting	Default	What it does
Young’s Modulus (Pa)	3,000,000	Scaled far below real concrete (3e10 Pa).
Tensile Strength (Pa)	20,000	Tension at which a crack starts.
Fracture Energy (J/m²)	5	Energy a crack absorbs per area. Low snaps like glass. High crumbles.
Density (kg/m³)	2400	Concrete.

All settings, with their tooltips, are in the Materials reference.