Materials & Surfaces

Define material properties and surface characteristics for your FDS simulations.

Overview

Surfaces (SURF) define boundary conditions and material properties. Materials (MATL) define the physical properties of solids.

from pyfds.core.namelists import Surface, Material

# Simple fire surface
sim.add(Surface(id='FIRE', hrrpua=1000.0))

# Material surface
sim.add(Material(id='WOOD', conductivity=0.12, specific_heat=1.0, density=500.0))
sim.add(Surface(id='WOOD_WALL', matl_id='WOOD', thickness=0.02))

Surface Types

Fire Surfaces

For combustion sources:

sim.add(Surface(
    id='BURNER',
    hrrpua=1000.0,      # Heat release rate per unit area (kW/m²)
    color='RED'          # Visualization color
)

See Fire Sources for detailed fire surface information.

Material Surfaces

For walls, floors, objects:

# Define material
sim.add(Material(
    id='CONCRETE',
    conductivity=1.8,    # Thermal conductivity (W/m·K)
    specific_heat=0.88,  # Specific heat (kJ/kg·K)
    density=2400.0       # Density (kg/m³)
)

# Create surface with material
sim.add(Surface(
    id='CONCRETE_WALL',
    matl_id='CONCRETE',
    thickness=0.2  # meters
)

Predefined Surfaces

FDS includes predefined surfaces:

• INERT - Adiabatic, non-reactive (default)
• OPEN - Open to ambient
• MIRROR - Symmetry plane
• PERIODIC - Periodic boundary
• HVAC - HVAC vent

# Use predefined
sim.add(Obstruction(xb=Bounds3D.of(0, 1, 0, 1, 0, 1), surf_ids=('INERT', 'INERT', 'INERT')))

Material Properties

Basic Material

sim.add(Material(
    id='MATERIAL_NAME',
    conductivity=0.5,    # W/m·K
    specific_heat=1.0,   # kJ/kg·K
    density=500.0        # kg/m³
)

Common Materials

# Gypsum board
sim.add(Material(
    id='GYPSUM',
    conductivity=0.48,
    specific_heat=0.84,
    density=1440.0
)

# Wood (generic)
sim.add(Material(
    id='WOOD',
    conductivity=0.12,
    specific_heat=1.0,
    density=500.0
)

# Steel
sim.add(Material(
    id='STEEL',
    conductivity=45.8,
    specific_heat=0.46,
    density=7850.0
)

# Concrete
sim.add(Material(
    id='CONCRETE',
    conductivity=1.8,
    specific_heat=0.88,
    density=2400.0
)

# Insulation
sim.add(Material(
    id='INSULATION',
    conductivity=0.04,
    specific_heat=0.84,
    density=100.0
)

Multi-Layer Surfaces

Composite Wall

# Define each material layer
sim.add(Material(id='GYPSUM', conductivity=0.48, specific_heat=0.84, density=1440.0))
sim.add(Material(id='INSULATION', conductivity=0.04, specific_heat=0.84, density=100.0))

# Create surface with multiple layers
sim.add(Surface(
    id='COMPOSITE_WALL',
    matl_id=['GYPSUM', 'INSULATION', 'GYPSUM'],  # Inside to outside
    thickness=[0.0127, 0.10, 0.0127]             # Thickness of each layer (m)
)

Temperature-Dependent Properties

Conductivity vs Temperature

Using RAMP for temperature-dependent conductivity:

# Conductivity ramp (temperature in °C, conductivity factor)
sim.add(Ramp(
    id='K_RAMP',
    t=[20, 100, 200, 400, 600],          # Temperature (°C)
    f=[1.0, 1.1, 1.3, 1.6, 2.0]          # Conductivity multiplier
)

sim.add(Material(
    id='TEMP_DEP_MATL',
    conductivity=0.5,
    specific_heat=1.0,
    density=1000.0,
    conductivity_ramp='K_RAMP'
)

Surface Colors

For visualization in Smokeview:

# Named colors
sim.add(Surface(id='FIRE', hrrpua=1000.0, color='RED'))
sim.add(Surface(id='WALL', matl_id='CONCRETE', thickness=0.2, color='GRAY'))

# RGB values (0-255)
sim.add(Surface(id='CUSTOM', matl_id='WOOD', thickness=0.02, rgb=(139, 69, 19)))

Common colors: RED, ORANGE, YELLOW, GREEN, BLUE, GRAY, BLACK, WHITE

Heat Transfer Properties

Emissivity

sim.add(Surface(
    id='BLACK_SURFACE',
    matl_id='STEEL',
    thickness=0.005,
    emissivity=0.95  # 0.0 to 1.0
)

sim.add(Surface(
    id='SHINY_SURFACE',
    matl_id='ALUMINUM',
    thickness=0.003,
    emissivity=0.09  # Polished aluminum
)

Backing Condition

# Insulated backing
sim.add(Surface(
    id='INSULATED_WALL',
    matl_id='CONCRETE',
    thickness=0.2,
    backing='INSULATED'  # No heat loss through back
)

# Exposed backing (default)
sim.add(Surface(
    id='EXPOSED_WALL',
    matl_id='CONCRETE',
    thickness=0.2,
    backing='EXPOSED'  # Heat loss to ambient
)

Complete Examples

Basic Wall Material

from pyfds import Simulation
from pyfds.core.namelists import Mesh, Material, Surface, Obstruction
from pyfds.core.geometry import Bounds3D, Grid3D

sim = Simulation(chid='wall_material')
sim.add(Mesh(ijk=Grid3D.of(50, 50, 25), xb=Bounds3D.of(0, 5, 0, 5, 0, 2.5)))

# Define gypsum material
sim.add(Material(
    id='GYPSUM',
    conductivity=0.48,
    specific_heat=0.84,
    density=1440.0
)

# Create surface with gypsum
sim.add(Surface(
    id='GYPSUM_WALL',
    matl_id='GYPSUM',
    thickness=0.0127,  # 1/2 inch
    color='WHITE'
)

# Apply to walls
sim.add(Obstruction(xb=Bounds3D.of(0, 0.2, 0, 5, 0, 2.5), surf_ids=('GYPSUM_WALL', 'INERT', 'INERT')))

sim.write('wall_material.fds')

Multi-Layer Wall

from pyfds import Simulation
from pyfds.core.namelists import Mesh, Material, Surface, Obstruction
from pyfds.core.geometry import Bounds3D, Grid3D

sim = Simulation(chid='composite_wall')
sim.add(Mesh(ijk=Grid3D.of(50, 40, 25), xb=Bounds3D.of(0, 5, 0, 4, 0, 2.5)))

# Define materials
sim.add(Material(id='GYPSUM', conductivity=0.48, specific_heat=0.84, density=1440.0))
sim.add(Material(id='INSULATION', conductivity=0.04, specific_heat=0.84, density=100.0))
sim.add(Material(id='WOOD_STUD', conductivity=0.12, specific_heat=1.0, density=500.0))

# Composite wall: gypsum-insulation-gypsum
sim.add(Surface(
    id='EXTERIOR_WALL',
    matl_id=['GYPSUM', 'INSULATION', 'GYPSUM'],
    thickness=[0.0127, 0.089, 0.0127],  # Total: ~0.115m
    color='TAN'
)

# Apply to wall
sim.add(Obstruction(xb=Bounds3D.of(0, 0.2, 0, 4, 0, 2.5), surf_ids=('EXTERIOR_WALL', 'INERT', 'INERT')))

sim.write('composite_wall.fds')

Temperature-Dependent Material

from pyfds import Simulation
from pyfds.core.namelists import Mesh, Ramp, Material, Surface, Obstruction
from pyfds.core.geometry import Bounds3D, Grid3D

sim = Simulation(chid='temp_dependent')
sim.add(Mesh(ijk=Grid3D.of(30, 30, 15), xb=Bounds3D.of(0, 3, 0, 3, 0, 1.5)))

# Conductivity increases with temperature
sim.add(Ramp(
    id='K_VS_T',
    t=[20, 200, 400, 600],
    f=[1.0, 1.2, 1.5, 2.0]
)

# Material with temperature-dependent conductivity
sim.add(Material(
    id='TEMP_MATL',
    conductivity=0.5,
    specific_heat=1.0,
    density=1000.0,
    conductivity_ramp='K_VS_T'
)

sim.add(Surface(
    id='TEMP_SURF',
    matl_id='TEMP_MATL',
    thickness=0.05
)

# Fire and wall
sim.add(Surface(id='FIRE', hrrpua=1000.0))
sim.add(Obstruction(xb=Bounds3D.of(1, 2, 1, 2, 0, 0.1), surf_ids=('FIRE', 'INERT', 'INERT')))
sim.add(Obstruction(xb=Bounds3D.of(0, 0.1, 0, 3, 0, 1.5), surf_ids=('TEMP_SURF', 'INERT', 'INERT')))

sim.write('temp_dependent.fds')

Best Practices

1. Use Realistic Material Properties

Reference material property databases: - SFPE Handbook - Engineering Toolbox - NIST material database

2. Match Physical Thickness

# Actual 1/2" gypsum board
sim.add(Surface(
    id='GYPSUM_WALL',
    matl_id='GYPSUM',
    thickness=0.0127  # 0.5 inches = 0.0127 m
)

3. Consider Thermal Penetration

Thickness should be greater than thermal penetration depth:

# δ ≈ √(α × t) where α = k/(ρ×c)
# For 600s simulation and concrete:
# α = 1.8 / (2400 × 0.88) ≈ 8.5×10⁻⁷ m²/s
# δ ≈ √(8.5×10⁻⁷ × 600) ≈ 0.023 m

# Use thickness > δ
sim.add(Surface(
    id='CONCRETE_WALL',
    matl_id='CONCRETE',
    thickness=0.05  # > 0.023 m
)

4. Document Sources

# Clear documentation
# Material properties from: SFPE Handbook, 5th Ed., Table X.Y
sim.add(Material(
    id='CONCRETE',
    conductivity=1.8,     # W/m·K
    specific_heat=0.88,   # kJ/kg·K
    density=2400.0        # kg/m³
)

Common Material Properties

Material	k (W/m·K)	c (kJ/kg·K)	ρ (kg/m³)
Gypsum	0.48	0.84	1440
Concrete	1.8	0.88	2400
Wood (oak)	0.17	1.7	700
Wood (pine)	0.12	1.0	500
Steel	45.8	0.46	7850
Aluminum	237	0.90	2700
Glass	0.76	0.84	2500
Brick	0.69	0.84	1920
Insulation	0.04	0.84	100

Pyrolysis Materials

Materials can thermally decompose (pyrolyze) producing gaseous fuel vapors and solid residues.

Single-Reaction Pyrolysis

Simple material that decomposes into one product:

from pyfds.builders import MaterialBuilder

# PMMA pyrolysis
pmma = (
    MaterialBuilder("PMMA")
    .density(1200)
    .thermal_conductivity(0.19)
    .specific_heat(1.4)
    .with_pyrolysis_product("MMA_VAPOR", yield_fraction=1.0)
    .with_heat_of_combustion(25000)
    .build()
)

sim.add_material(pmma)

Multi-Reaction Pyrolysis

Materials with complex decomposition (e.g., wood → vapor + char):

# Wood decomposition
wood = (
    MaterialBuilder("WOOD")
    .density(500)
    .thermal_conductivity(0.13)
    .specific_heat(2.5)
    .add_pyrolysis_reaction(
        a=1e10,                      # Pre-exponential factor (1/s)
        e=100000,                    # Activation energy (kJ/kmol)
        heat_of_reaction=1800,       # Heat absorbed (kJ/kg)
        product_species="WOOD_VAPOR" # Gas product
    )
    .add_pyrolysis_reaction(
        a=5e8,
        e=120000,
        heat_of_reaction=500,
        residue_material="CHAR"      # Solid residue
    )
    .build()
)

# Char material (solid residue)
char = (
    MaterialBuilder("CHAR")
    .density(200)
    .thermal_conductivity(0.08)
    .specific_heat(1.0)
    .build()
)

sim.add_material(wood)
sim.add_material(char)

Predefined Materials

Use common materials with validated properties:

# Pre-configured materials
concrete = MaterialBuilder.concrete()
steel = MaterialBuilder.steel()
wood = MaterialBuilder.wood()
gypsum = MaterialBuilder.gypsum()
aluminum = MaterialBuilder.aluminum()
brick = MaterialBuilder.brick()

# Add to simulation
sim.add_material(concrete)
sim.add_material(steel)

Pyrolysis Parameters

Kinetics: - a: Pre-exponential factor (1/s) - typical range: 1e8 to 1e12 - e: Activation energy (kJ/kmol) - typical range: 80,000 to 200,000 - heat_of_reaction: Energy absorbed during pyrolysis (kJ/kg)

Products: - product_species: Gas species ID produced - residue_material: Solid material ID remaining - yield_fraction: Fraction of original material yielded (0-1) - reaction_order: Reaction order (default: 1.0)

Surface Particle Generation

Surfaces can generate particles (e.g., smoke from fires, water from sprinklers):

from pyfds.builders import SurfBuilder

# Fire generating smoke
fire_surf = (
    SurfBuilder("FIRE")
    .with_heat_release(1000.0, ramp_id="fire_growth")
    .with_particle_generation("SMOKE", mass_flux=0.002, nppc=2)
    .with_color("ORANGE")
    .build()
)

# Sprinkler generating water droplets
sprinkler_surf = (
    SurfBuilder("SPRINKLER")
    .as_sprinkler(
        part_id="WATER_DROP",
        mass_flux=0.02,
        median_diameter=0.001,
        velocity=6.0
    )
    .build()
)

sim.add_surface(fire_surf)
sim.add_surface(sprinkler_surf)

See Particles and Suppression Systems for details.

Next Steps

• Fire Sources - Creating fires
• Particles - Particle systems
• Suppression Systems - Sprinkler systems
• RAMP Guide - Temperature-dependent properties
• Combustion - Fuel properties

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Particles Guide →