When nParticles are created or emitted, they appear in the simulation with a radius value set by the Radius attribute. You can vary nParticle Radius during the simulation by setting the Radius Scale ramp. The Radius Scale ramp allows you to map per-particle Radius values to nParticle properties such as Particle ID, Age, and Speed.

To set nParticle Radius

1. In the scene view, select the nParticle object you want to edit.
2. In the Attribute Editor, select the nParticle object’s nParticleShape tab.
3. In the Particle Size section, set the Radius value.

To set the Radius Scale ramp

1. In the scene view, select the nParticle object for which you want to set a Radius Scale ramp.
2. In the Radius Scale section of the nParticleShape node Attribute Editor, create the radius value curve by setting values for Selected Position and Selected Value.

   For more information about the Radius Scale ramp, see Radius Scale.

3. Set an Interpolation method to determine how particle radius blends between each position on the ramp. See Interpolation.
4. Set Radius Scale Input to determine which attribute is used as the input attribute for the Radius Scale ramp. See Radius Scale Input.
5. (Optional) Set Input Max to define the range of the Radius Scale ramp. See Input Max.
6. (Optional) Set the Radius Scale Randomize to add a randomized multiplier to per-particle Radius values. See Radius Scale Randomize.