Pyro Physics, Motion and Combustion¶

Configure transport, boundaries, dissipation, motion detail, combustion and Pyro Data Mapping.

The Physics tab controls simulation channels, timing, Dense domain boundaries, and the behavior and appearance of smoke, fire, heat, color, turbulence, dissipation, diffusion, and combustion. These are the main artist controls after the emitter setup is in place.

Lists and Nodes¶

Lists present these controls together in the Physics tab. Nodes divide them by responsibility in the executable Pyro chain: Pyro Dynamics contains timing, environment, dissipation and softening; Pyro Motion Detail contains swirl, turbulence and shredding; Pyro Combustion contains burning and flame behavior; Pyro Boundaries contains Dense side controls. Connect only the stages needed by the graph. Fire-dependent Combustion controls require Fire to be enabled on Pyro Domain. Each stage's complete controls are available in the Inspector.

Simulation Channels & Timing¶

• Fire Channels: stores fuel and flame for combustion workflows. Disable it when fire data is not needed to reduce memory use.
• Color Channel: stores and transports colored smoke. Disable it when color advection is not needed.
• Time Scale: speeds up or slows down the entire simulation.

Dense Domain Boundaries¶

Fast Dense can assign a different boundary behavior to each side of the domain. Ready-made setups keep common workflows simple, while individual sides can still be adjusted when needed.

• Setup: quickly configures an Open Domain, Wind Tunnel, Slip Box, or Solid Box. Choosing a side manually switches the setup to Custom.
• Per-side controls: X-, X+, Y-, Y+, Z-, and Z+ each choose their own boundary mode.
• Open: lets smoke and airflow leave the selected side and prevents unwanted flow back into the domain.
• Inflow: continuously feeds controlled airflow into the domain. Use Into Domain with a Speed for the common case, or Custom for a velocity vector. If more than one side uses Inflow, the side buttons under Inflow Settings select the Inflow Side whose Direction, Speed/Velocity, and injected content are being edited.
• Injected Content: optionally carries Smoke, Temperature, Fuel, and Flame with an inflow. Fuel and Flame controls are shown when Fire Channels are enabled.
• Slip Wall: keeps the flow inside while allowing it to slide along the wall.
• Solid Wall: keeps the flow inside and stops motion along the wall.
• Start With Flow: with a single inflow, fills a fresh Dense simulation with that inflow velocity so wind-tunnel style setups do not begin in still air.

Environment¶

• Ambient Heat: background heat of the scene. Higher values reduce how much hot smoke rises.
• Buoyancy: how strongly hot smoke and fire rise.
• Smoke Weight: how strongly dense smoke reacts to gravity.
• Gravity: vertical gravity for smoke and fire. Negative values pull smoke downward; 0 creates floating motion.

Swirl & Turbulence¶

• Swirl Detail: restores rolling and curling smoke detail.
• Large Swirls: Fast Dense only. Adds broader rolling motion.
• Large Swirl Size: Fast Dense only. Size of the broad smoke rolls.
• Baroclinic Torque: creates vortices where hot and cold areas meet, useful for fire edges.
• Turbulence: strength of the background turbulence field. It affects active smoke, heat, fuel, and flame regions in both Sparse and Fast Dense.
• Turbulence Size: scale of the turbulence pattern.
• Turbulence Speed: how quickly the turbulence changes over time.

Shredding in Sparse Advanced¶

Shredding adds block-shaped random velocity disturbances that split smoke and fire into smaller streaks. It is available only with Sparse Advanced. Start with a low Strength, establish the visible scale with Block Size, and then adjust animation. Shredding changes motion, so it is not a substitute for a smaller Voxel Size when the simulation itself lacks spatial resolution.

• Strength: amount of shredding motion. 0 disables the feature.
• Block Size: world-space size of each disturbance region. Smaller values produce finer breakup and larger values produce broader blocks.
• Speed: how quickly the random pattern changes over time.
• Seed: selects a different pattern without changing its scale or strength.
• Cutoff Field: optionally limits shredding with Smoke, Heat, Fuel, Velocity, Smoke + Heat, or Smoke + Fuel. Off applies it throughout active voxels.
• Threshold: with a Cutoff Field selected, shredding is applied where that field is below the threshold. Raise it to admit more of the selected field's value range.

Use the cutoff to keep shredding out of the densest or most energetic part of a plume while breaking up its weaker regions. For example, a Smoke cutoff can leave the dense core more coherent and disturb lower-density edges. Fuel-based cutoffs require meaningful fuel data from a fire setup.

Advanced Motion Detail¶

• Swirl Update Rate: how often swirl detail is refreshed.
• Quiet Area Protection: Fast Dense only. Protects calm smoke areas from artificial over-curling.
• Base Swirl Mask: Fast Dense only. Base amount of swirl allowed before other influences are added.
• Speed Influence: Fast Dense only. Adds more swirl to faster-moving smoke.
• Heat Influence: Fast Dense only. Adds more swirl to hotter areas.
• Smoke Influence: Fast Dense only. Adds more swirl where smoke density is stronger.
• Minimum Heat / Maximum Heat: Fast Dense only. Heat range allowed to receive swirl.
• Minimum Smoke / Maximum Smoke: Fast Dense only. Density range allowed to receive swirl.
• Octaves: number of turbulence detail layers.
• Lacunarity: spacing between turbulence layers.
• Gain: strength of smaller turbulence layers.
• Random Seed: changes the turbulence pattern.

Dissipation¶

• Smoke / Smoke Fade: how quickly smoke density disappears.
• Color / Color Fade: how quickly colored smoke loses its color.
• Heat / Heat Cooldown: how quickly hot areas cool down.
• Motion / Motion Damping: how quickly velocity loses energy.
• Fuel / Fuel Fade: how quickly unburned fuel disappears. In Sparse mode, fuel also keeps the active domain alive, so use non-zero fuel dissipation for short-lived fire sources.
• Flame / Flame Fade: how quickly visible flame dies out.

In Sparse mode, actively dissipating channels are cleared once only sub-visible numerical tails remain. This prevents faded smoke, flame, or fuel from extending and retaining sparse leaves indefinitely.

Softening¶

• Smoke / Smoke Softening: smooths smoke density over time.
• Heat / Heat Softening: smooths and spreads heat.
• Fuel / Fuel Softening: smooths and spreads fuel.
• Flame / Flame Softening: smooths visible flame structures.
• Viscosity / Motion Softening: diffuses momentum over time. Higher values produce thicker, smoother motion.

Combustion¶

• Burn Rate: how fast fuel is consumed.
• Oxygen Loss: how strongly smoke suppresses combustion. Higher values make fire burn more on surfaces and edges.
• Burn Variation: random variation in the burn pattern.
• Ignition Heat: heat required to ignite fuel.
• Heat Release: heat produced by burning fuel.
• Expansion: gas expansion when fuel ignites.
• Flame Intensity: brightness and amount of visible flame.
• Smoke Release: smoke produced when fuel burns.
• Smoke Lift: upward velocity added to smoke created by combustion or flame extinction. It is applied in both Sparse and Fast Dense.
• Extinction Smoke: extra smoke created when flames go out. The slider covers the common 0-100 range; dense explosion plumes can use manually entered values up to 1000.
• Extinction Heat: heat level below which flames begin to extinguish.
• Fuel Loss: how much fuel is consumed by combustion.
• Flame Loss: how much visible flame is removed during extinction.
• Fuel Oxygen Premix: adds oxygen with fuel to change premixed flame behavior.
• Flame Oxygen Weight: how much existing flame reduces local oxygen for new burning.
• Ignition Progress: blends between hard ignition and progressive temperature-based ignition.
• Extinction Progress: blends between hard extinction and progressive extinction.
• Smoke Release Color: color tint for smoke produced by burning fuel.
• Extinction Color: color tint for smoke produced when flames extinguish.

Pyro Data Mapping¶

Mapping is available on Physics, supported Forces, and individual Sources. In Lists, use Add Mapping... to build an ordered stack and reorder, enable, or remove its layers there. In Nodes, choose Add Mapping... in the selected Pyro node’s Inspector: this creates a connected Mapping node for that parameter. Its source and Blend mode are visible on the node; further response controls are in its Inspector. You can also add a named source such as Pyro Map: Smoke Density or Pyro Map: Noise from Shift+A and connect it yourself. Disconnecting or deleting a Mapping node removes its influence without leaving a hidden layer behind. Each target has one Mapping input; connect Mapping nodes through Previous to create an ordered chain. Adding another Mapping extends that chain. Unsupported sources are shown as node errors. With Fast GPU Volume, changing a mapping keeps the already simulated frame visible; the new value affects the next simulated frame.

Mapping Response¶

• Source: chooses the field, spatial value, procedural value, time source, or emitter data that drives the target.
• Source Min / Max: input interval mapped to the output range.
• Outside Range: Clamp, Repeat, Ping-Pong, or Continue.
• Mapping Curve: optional editable response curve between the input and output ranges.
• Output Min / Max: values produced at the ends of the mapped range.
• Apply Mode: Multiply, Add, or Replace the value produced by layers above it.
• Influence: blends the mapping layer from no effect to full effect.

Physics Targets¶

• Motion: Swirl Detail, Large-Scale Swirl, Turbulence Strength, and Shredding Strength.
• Environment: Buoyancy and Smoke Weight.
• Dissipation: Smoke Dissipation, Heat Dissipation, Motion Dissipation, Color Dissipation, Fuel Dissipation, and Flame Dissipation.
• Combustion: Burn Rate, Heat Release, Fuel Expansion, Flame Production, Smoke Release, and Smoke Lift.

Effect Targets¶

• Wind: Strength and Acceleration.
• Follow Curve: Strength and Attract.
• Sink: Absorption and Velocity Damping.

Emitter Targets¶

• Emission: Smoke, Temperature, Fuel, Flame, and Pressure.
• Color: Color R, Color G, and Color B.

Sources¶

• Pyro Fields: Density, Temperature, Fuel, Flame, Pressure, Color Luminance, Color R, Color G, and Color B. Fire/Color sources appear only when their simulation channels and mapping context support them.
• Velocity: Speed, Velocity X, Velocity Y, and Velocity Z.
• Space: Position X, Position Y, Position Z, and Distance. Distance exposes Distance From for an Empty.
• Procedural: Noise with Scale, Animation Speed, Detail, and Seed.
• Time: Scene Time, Simulation Time, or Normalized Simulation; non-normalized modes expose Unit = Frames/Seconds. Emitter mappings additionally offer Emitter Time.
• Emitter-only data: Vertex Weight, Color Attribute Luminance/R/G/B/A, and Particle Color Luminance/R/G/B. These sources appear only when the selected emitter type exposes the required weight, Geometry Nodes color, or particle-color data; Geometry Nodes color mapping uses the emitter’s Attribute name.

Emitter mappings use source/emitter data before it enters the Pyro grid; Physics and Effect mappings can use simulated grid fields. Sparse mode hides grid sources that are not available in the active pass.