---
title: Particle Attributes
description: "Particle Attributes can be used in expressions if the channel is marked with an „@„. There are Scalar (one Value) or Vector (three Values) Attributes available. You can both read the values or write them for example with the \"Attribute-Set\"-Node.…"
url: "https://storm-vfx.com/docs/particle-attributes/"
updated: "2022-05-26"
category: General / Expressions
---

# Particle Attributes

Particle Attributes can be used in expressions if the channel is marked with an „@„. There are Scalar (one Value) or Vector (three Values) Attributes available. You can both read the values or write them for example with the "Attribute-Set"-Node. To access one of the three vector values you have to add a dot and the value you desire. 

So if you want to read velocity in x direction use „@v.x“.

| Attribute | Explanation |
| --- | --- |
| @ptnum | returns index of a particle |
| @numpt | returns number of a particles |
| @id | returns id of a particle (if available) |
| @Cd | Color of a particle @Cd.x (Red Channel) @Cd.y (Green Channel) @Cd.z (Blue Channel) |
| @v | Velocity vector @v.x (X-Axis) @v.y (Y-Axis) @v.z (Z-Axis) |
| @P | Current Position of a Particle @P.x (X-Axis) @P.y (Y-Axis) @P.z (Z-Axis) |

**set Particle Attributes**

you can set custom particle attributes with the „Attribute-Set“ Node. You can use your own terms, but a few are already in use by the system.

| Attribute | Explanation |
| --- | --- |
| „force“  | A vector which defines the Force per Particle does not import from the classic systems but you can write to set a per particle force |
| „width“ | The size of each particle (does not affect the simulation) |
| „id“ | Id of each particle can be read, but not written |
| „emissionPos“ | The Position at the moment of particlecreation |
| „sleeping“ | Is the particle asleep or not |
| „stick“ | Is the particle sticking or not |
| „emitterId“ | returns an id from the emitter that created that particle |

**Solver specific attributes** - Granular (CPU only)

| Attribute | Explanation |
| --- | --- |
| „maxStretch“  | Sets how much stretching is tolerated before contraints are breaking |

**Solver specific attributes** - SPH (CPU only)

| Attribute | Explanation |
| --- | --- |
| „viscosity“ | controls the viscosity of the fluid per particle |
| „surfaceTension“ | controls the surface tension of the fluid per particle |

**Solver specific attributes** - Cloth

| Attribute | Explanation |
| --- | --- |
| „breakstretch“  | controls how much stretching is allowed before breaking the constraints |
| „stiffness“  | sets the stiffness of the constraints generated from the particles |