ForMatter/Materials/polymer/Expanded Polystyrene Foam (EPS)
mat_eps_foam

Expanded Polystyrene Foam (EPS)

thermoplastic foam — closed-cell, bead-fused · EPS, Styrofoam (genericized), white bead foam, model-shop foam, packing foam
mediumlast updated 2026-04-28
metallic 0.00
hue shift +0°

White, light, squeaky when rubbed. The foam every fragile shipped object arrives in. In the model shop it's the cheap block you cut with a hot wire to mock up a form before you commit. Crumbles into a static-charged mess when sawn dry; sands to a snowfall.

Polystyrene beads expanded with pentane and steam-fused into a 95–98% air closed-cell foam. Density 12–35 kg/m³ depending on bead loading. Compressive strength scales with density (50–200 kPa at 10% deformation). Excellent thermal insulation (k ≈ 0.033–0.040 W/m·K). Solvents (acetone, MEK, most spray paints with hydrocarbon propellants) dissolve it instantly; water-based finishes are safe.

physical

  • density_kg_m324
  • compressive_strength_kpa110
  • thermal_conductivity_w_mk0.036
source: Wikipedia — Expanded polystyrene

Sustainability

  • recyclabilitylow — recycle code 6 but rarely collected curbside; densifier programs exist regionally; banned in foodservice in many US cities
  • biodegradableFalse
  • certifications—
visual
matte, optical-white, the bead boundaries visible on any cut surface
tactile
cool but warmer than polymer (it's mostly air), squeaks against itself
weight perception
almost nothing
acoustic
the squeak — the unmistakable sound of packaging foam against packaging foam

PBR starter values

Principled BSDF defaults derived from the sphere granular finish. Reasonable seed for Blender, Substance, Keyshot, Rhino — tune per material.

# finish:      granular
albedo        #f4f0e8
metallic      0.00
roughness     0.85
ior           1.45
transmission  0.00
clearcoat     0.00
sheen         0.00
anisotropic   0.00
copy as JSON 
{
  "albedo": "#f4f0e8",
  "metallic": 0.0,
  "roughness": 0.85,
  "ior": 1.45,
  "transmission": 0.0,
  "clearcoat": 0.0,
  "sheen": 0.0,
  "anisotropic": 0.0
}
Blender 4.x Python 
# Blender 4.x — Principled BSDF
# Expanded Polystyrene Foam (EPS) · finish: granular
import bpy
mat = bpy.data.materials.new(name="mat_eps_foam")
mat.use_nodes = True
bsdf = mat.node_tree.nodes["Principled BSDF"]
bsdf.inputs["Base Color"].default_value         = (0.9047, 0.8714, 0.807, 1.0)
bsdf.inputs["Metallic"].default_value           = 0.000
bsdf.inputs["Roughness"].default_value          = 0.850
bsdf.inputs["IOR"].default_value                = 1.450
bsdf.inputs["Transmission Weight"].default_value = 0.000
bsdf.inputs["Coat Weight"].default_value        = 0.000
bsdf.inputs["Sheen Weight"].default_value       = 0.000
bsdf.inputs["Anisotropic"].default_value        = 0.000
KeyShot Python (lux) 
# KeyShot 11+ — lux Python API, Generic material
# Expanded Polystyrene Foam (EPS) · finish: granular
# Run from Window → Scripting Console
import lux
mat = lux.createMaterial(name="mat_eps_foam", materialType="Generic")
mat.setProperty("diffuse",      (244, 240, 232))   # 8-bit sRGB
mat.setProperty("metallic",     0.000)
mat.setProperty("roughness",    0.850)
mat.setProperty("indexOfRefraction", 1.450)
mat.setProperty("transparency", 0.000)
mat.setProperty("coatingWeight", 0.000)
Substance pbrMetalRough 
{
  "_format": "Substance Designer / Painter \u2014 pbrMetalRough constants",
  "_about": "Expanded Polystyrene Foam (EPS) \u00b7 finish: granular",
  "baseColor": {
    "r": 0.9047,
    "g": 0.8714,
    "b": 0.807
  },
  "metallic": 0.0,
  "roughness": 0.85,
  "ior": 1.45,
  "opacity": 1.0,
  "anisotropyLevel": 0.0,
  "_notes": "Channels listed are the standard Substance pbrMetalRough output. Drop into a Uniform Color node per channel, or as the constant input on a layered stack."
}
glTF 2.0 Metallic-Roughness 
{
  "asset": {
    "version": "2.0",
    "generator": "ForMatter"
  },
  "materials": [
    {
      "name": "mat_eps_foam",
      "pbrMetallicRoughness": {
        "baseColorFactor": [
          0.9047,
          0.8714,
          0.807,
          1.0
        ],
        "metallicFactor": 0.0,
        "roughnessFactor": 0.85
      },
      "extensions": {
        "KHR_materials_ior": {
          "ior": 1.45
        }
      }
    }
  ]
}
USD Preview Surface 
# USD Preview Surface — UsdShade.MaterialLook prim attributes
# Expanded Polystyrene Foam (EPS) · finish: granular
def Material "mat_eps_foam" {
    token outputs:surface.connect = </mat_eps_foam/PreviewSurface.outputs:surface>

    def Shader "PreviewSurface" {
        uniform token info:id = "UsdPreviewSurface"
        color3f inputs:diffuseColor = (0.9047, 0.8714, 0.807)
        float   inputs:metallic     = 0.000
        float   inputs:roughness    = 0.850
        float   inputs:ior          = 1.450
        float   inputs:opacity      = 1.000
        float   inputs:clearcoat    = 0.000
        token   outputs:surface
    }
}
↓ download glTF material
ProcessCNC Milling · Hot-Wire Foam Cutting
Used inFood Packaging · Prototype / Concept Model
Substitutes
Extruded Polystyrene Foam (XPS)
Mycelium Composite (Grown)

Citations