---

name: ifcos-impl-materials description: > Use when assigning materials to IFC elements -- single materials, layer sets (walls), profile sets (beams/columns), or constituent sets (IFC4+). Prevents the common mistake of using IfcMaterialConstituentSet in IFC2X3 (not available). Covers IfcMaterial, IfcMaterialLayerSet, IfcMaterialProfileSet, material properties, and presentation. Keywords: material, IfcMaterial, layer set, profile set, constituent set, material assignment, IfcMaterialLayerSet, IfcMaterialProfileSet, material properties, assign material, wall layers. license: MIT compatibility: "Designed for Claude Code. Requires IfcOpenShell Python library." metadata: author: OpenAEC-Foundation version: "1.0"

IFC Material Assignment Implementation Guide

Quick Reference

Decision Tree: Which Material Type to Use

What kind of element needs material?
├── Single homogeneous material (e.g., steel column, concrete beam)?
│   └── IfcMaterial → assign_material(type="IfcMaterial")
│
├── Layered construction (wall, slab, roof with defined layers)?
│   └── IfcMaterialLayerSet → add_material_set(set_type="IfcMaterialLayerSet")
│       └── Each layer has a thickness (LayerThickness in meters)
│
├── Profiled structural element (beam, column with cross-section)?
│   └── IfcMaterialProfileSet → add_material_set(set_type="IfcMaterialProfileSet")
│       └── Each profile has an IfcProfileDef defining the cross-section
│
├── Composite element with named parts (window: frame+glazing)?
│   ├── IFC4+ → IfcMaterialConstituentSet
│   │   └── add_material_set(set_type="IfcMaterialConstituentSet")
│   └── IFC2X3 → IfcMaterialList (legacy, no named parts)
│       └── add_material_set(set_type="IfcMaterialList")
│
└── Legacy unordered material list (IFC2X3 only)?
    └── IfcMaterialList → add_material_set(set_type="IfcMaterialList")

Decision Tree: Assign Material to Type or Occurrence?

Where to assign the material?
├── Element type (IfcWallType, IfcSlabType, etc.)? [RECOMMENDED]
│   └── Assign to type → all occurrences inherit the material
│       └── ifcopenshell.api.material.assign_material(model,
│           products=[wall_type], type="IfcMaterialLayerSet", material=layer_set)
│
└── Individual occurrence (IfcWall, IfcSlab, etc.)?
    └── Assign to occurrence → overrides type material for this element only
        └── ifcopenshell.api.material.assign_material(model,
            products=[wall], material=concrete)

Critical Warnings

• ALWAYS assign materials to element types (IfcWallType, IfcSlabType), not individual occurrences. Occurrences inherit from their type. Assign to occurrences only when overriding type material.
• ALWAYS use ifcopenshell.api.material.* functions for material operations. NEVER create IfcMaterial or IfcRelAssociatesMaterial entities directly with create_entity().
• NEVER use IfcMaterialConstituentSet with IFC2X3 schema. It does not exist in IFC2X3. Use IfcMaterialList instead.
• ALWAYS check model.schema before using schema-specific material types.
• NEVER assign multiple materials directly to the same product. Use material sets (layer, profile, constituent) for composite materials. assign_material() automatically unassigns previous materials.
• ALWAYS set LayerThickness on layers after creation using edit_layer(). Layers without thickness are invalid.
• ALWAYS provide a profile definition (IfcProfileDef) when adding profiles to a profile set. A material profile without a profile curve is incomplete.
• NEVER set material relationships via direct attribute assignment (e.g., wall.HasAssociations = ...). ALWAYS use the API.

---

Essential Patterns

Pattern 1: Create and Assign a Single Material

# IfcOpenShell: all schema versions
import ifcopenshell
import ifcopenshell.api

# Create a material with category
concrete = ifcopenshell.api.material.add_material(model,
    name="Concrete C30/37", category="concrete")

# Assign to a wall (single material, no layers)
ifcopenshell.api.material.assign_material(model,
    products=[wall], material=concrete)

Pattern 2: Create a Layered Wall Material (IfcMaterialLayerSet)

# IfcOpenShell: all schema versions
import ifcopenshell.api

# Step 1: Create individual materials
brick = ifcopenshell.api.material.add_material(model,
    name="Facing Brick", category="brick")
insulation = ifcopenshell.api.material.add_material(model,
    name="Mineral Wool", category="glass")
block = ifcopenshell.api.material.add_material(model,
    name="Concrete Block", category="block")

# Step 2: Create layer set container
layer_set = ifcopenshell.api.material.add_material_set(model,
    name="External Wall 300mm", set_type="IfcMaterialLayerSet")

# Step 3: Add layers (order = outside to inside)
layer1 = ifcopenshell.api.material.add_layer(model,
    layer_set=layer_set, material=brick)
ifcopenshell.api.material.edit_layer(model,
    layer=layer1, attributes={"LayerThickness": 0.102})

layer2 = ifcopenshell.api.material.add_layer(model,
    layer_set=layer_set, material=insulation)
ifcopenshell.api.material.edit_layer(model,
    layer=layer2, attributes={"LayerThickness": 0.100})

layer3 = ifcopenshell.api.material.add_layer(model,
    layer_set=layer_set, material=block)
ifcopenshell.api.material.edit_layer(model,
    layer=layer3, attributes={"LayerThickness": 0.100})

# Step 4: Assign to wall TYPE (best practice)
ifcopenshell.api.material.assign_material(model,
    products=[wall_type], type="IfcMaterialLayerSet", material=layer_set)

Pattern 3: Create a Profiled Beam Material (IfcMaterialProfileSet)

# IfcOpenShell: all schema versions
import ifcopenshell.api

# Step 1: Create material
steel = ifcopenshell.api.material.add_material(model,
    name="S355", category="steel")

# Step 2: Create profile set
profile_set = ifcopenshell.api.material.add_material_set(model,
    name="HEA 200", set_type="IfcMaterialProfileSet")

# Step 3: Create profile definition (cross-section shape)
profile_def = ifcopenshell.api.profile.add_parameterised_profile(model,
    ifc_class="IfcIShapeProfileDef",
    OverallWidth=0.200, OverallDepth=0.190,
    WebThickness=0.0065, FlangeThickness=0.010)

# Step 4: Add profile item to set
profile_item = ifcopenshell.api.material.add_profile(model,
    profile_set=profile_set, material=steel, profile=profile_def)

# Step 5: Assign to column TYPE
ifcopenshell.api.material.assign_material(model,
    products=[column_type], type="IfcMaterialProfileSet", material=profile_set)

Pattern 4: Constituent Set for Composite Elements (IFC4+ Only)

# IfcOpenShell: IFC4 and IFC4X3 ONLY (NOT IFC2X3)
import ifcopenshell.api

# Step 1: Create materials
aluminium = ifcopenshell.api.material.add_material(model,
    name="Aluminium Frame", category="aluminium")
glass = ifcopenshell.api.material.add_material(model,
    name="Double Glazing", category="glass")

# Step 2: Create constituent set
constituent_set = ifcopenshell.api.material.add_material_set(model,
    name="Window Assembly", set_type="IfcMaterialConstituentSet")

# Step 3: Add named constituents
frame = ifcopenshell.api.material.add_constituent(model,
    constituent_set=constituent_set, material=aluminium, name="Frame")
glazing = ifcopenshell.api.material.add_constituent(model,
    constituent_set=constituent_set, material=glass, name="Glazing")

# Step 4: Assign to window TYPE
ifcopenshell.api.material.assign_material(model,
    products=[window_type], type="IfcMaterialConstituentSet",
    material=constituent_set)

Pattern 5: Query Material from an Element

# IfcOpenShell: all schema versions
import ifcopenshell.util.element

# Get material (returns IfcMaterial, IfcMaterialLayerSet, etc.)
material = ifcopenshell.util.element.get_material(wall)

if material is None:
    print("No material assigned")
elif material.is_a("IfcMaterial"):
    print(f"Single material: {material.Name}")
elif material.is_a("IfcMaterialLayerSet"):
    for layer in material.MaterialLayers:
        print(f"Layer: {layer.Material.Name}, Thickness: {layer.LayerThickness}")
elif material.is_a("IfcMaterialLayerSetUsage"):
    layer_set = material.ForLayerSet
    for layer in layer_set.MaterialLayers:
        print(f"Layer: {layer.Material.Name}, Thickness: {layer.LayerThickness}")
elif material.is_a("IfcMaterialProfileSet"):
    for profile in material.MaterialProfiles:
        print(f"Profile: {profile.Material.Name}")
elif material.is_a("IfcMaterialConstituentSet"):
    for constituent in material.MaterialConstituents:
        print(f"Constituent: {constituent.Name} - {constituent.Material.Name}")

Pattern 6: Add Visual Style to a Material

# IfcOpenShell: all schema versions
import ifcopenshell.api

# Create a surface style (visual appearance)
style = ifcopenshell.api.style.add_style(model, name="Concrete Grey")
ifcopenshell.api.style.add_surface_style(model, style=style,
    ifc_class="IfcSurfaceStyleShading",
    attributes={
        "SurfaceColour": {"Name": None, "Red": 0.7, "Green": 0.7, "Blue": 0.7}
    })

# Assign style to a representation
ifcopenshell.api.style.assign_representation_styles(model,
    shape_representation=body_rep, styles=[style])

---

Common Operations

Material Categories (Standard Values)

Category	Use For
"concrete"	Concrete elements, precast
"steel"	Structural steel, reinforcement
"aluminium"	Window frames, curtain walls
"brick"	Masonry walls
"block"	Concrete blocks
"stone"	Natural stone elements
"wood"	Timber construction
"glass"	Glazing, insulation (glass wool)
"gypsum"	Plasterboard, gypsum finishes
"plastic"	PVC pipes, synthetic membranes
"earth"	Foundation fill, landscaping

Material Set Type Selection Guide

Element Type	Material Set	Schema
Walls (layered)	IfcMaterialLayerSet	All
Slabs (layered)	IfcMaterialLayerSet	All
Roofs (layered)	IfcMaterialLayerSet	All
Beams	IfcMaterialProfileSet	All
Columns	IfcMaterialProfileSet	All
Members	IfcMaterialProfileSet	All
Windows	IfcMaterialConstituentSet	IFC4+
Doors	IfcMaterialConstituentSet	IFC4+
Curtain walls	IfcMaterialConstituentSet	IFC4+
Furniture	IfcMaterial (single)	All
Equipment	IfcMaterial (single)	All
Windows (legacy)	IfcMaterialList	IFC2X3

Remove Material from Element

# IfcOpenShell: all schema versions
ifcopenshell.api.material.unassign_material(model, products=[wall])

Copy a Material with All Properties

# IfcOpenShell: all schema versions
new_material = ifcopenshell.api.material.copy_material(model,
    material=existing_material)
# Copies psets and styles. Set items are copied but underlying materials reused.

Edit Material Properties

# IfcOpenShell: all schema versions
ifcopenshell.api.material.edit_material(model,
    material=concrete, attributes={"Name": "Concrete C35/45", "Category": "concrete"})

Reorder Layers in a Layer Set

# IfcOpenShell: all schema versions
ifcopenshell.api.material.reorder_set_item(model,
    material_set=layer_set, old_index=2, new_index=0)

Edit Layer Usage (Offset from Reference Line)

# IfcOpenShell: all schema versions
# Get the usage from the element
material = ifcopenshell.util.element.get_material(wall)
if material.is_a("IfcMaterialLayerSetUsage"):
    ifcopenshell.api.material.edit_layer_usage(model,
        usage=material, attributes={"OffsetFromReferenceLine": -0.1})

Delete Material and Material Set

# IfcOpenShell: all schema versions
# First unassign from all products
ifcopenshell.api.material.unassign_material(model, products=[wall_type])

# Then remove the material set
ifcopenshell.api.material.remove_material_set(model, material_set=layer_set)

# Remove individual materials (only if not used elsewhere)
ifcopenshell.api.material.remove_material(model, material=brick)

---

Version Notes

IFC2X3 vs IFC4+ Material Differences

Feature	IFC2X3	IFC4 / IFC4X3
IfcMaterial	Yes	Yes
IfcMaterialLayerSet	Yes	Yes
IfcMaterialProfileSet	Yes	Yes
IfcMaterialConstituentSet	No	Yes
IfcMaterialList	Yes (primary)	Yes (legacy)
Material category attribute	No	Yes
Material description attribute	No	Yes

Schema-Aware Material Assignment

# IfcOpenShell: all schema versions
import ifcopenshell.util.element

if model.schema == "IFC2X3":
    # IFC2X3: Use IfcMaterialList for composite elements
    material_list = ifcopenshell.api.material.add_material_set(model,
        name="Window Materials", set_type="IfcMaterialList")
    ifcopenshell.api.material.add_list_item(model,
        material_list=material_list, material=aluminium)
    ifcopenshell.api.material.add_list_item(model,
        material_list=material_list, material=glass)
else:
    # IFC4+: Use IfcMaterialConstituentSet for named parts
    constituent_set = ifcopenshell.api.material.add_material_set(model,
        name="Window Assembly", set_type="IfcMaterialConstituentSet")
    ifcopenshell.api.material.add_constituent(model,
        constituent_set=constituent_set, material=aluminium, name="Frame")
    ifcopenshell.api.material.add_constituent(model,
        constituent_set=constituent_set, material=glass, name="Glazing")

---

Material + Style Integration

Materials define physical properties. Styles define visual appearance. These are separate concepts in IFC. ALWAYS apply both together for visual BIM models.

Workflow: Material + Visual Style

1. Create IfcMaterial → physical definition
2. Create IfcSurfaceStyle → visual appearance (color, texture)
3. Assign style to representation → visual display
4. Assign material to product → physical association

Materials and styles are NOT linked automatically. A material named "Concrete" does not automatically render as grey. The style must be explicitly created and assigned to the element's representation.

---

Reference Links

• API Method Signatures — Complete signatures for all material API methods
• Working Code Examples — End-to-end examples for all material operations
• Anti-Patterns — Common material assignment mistakes and how to avoid them