Blender Subsurface Weight vs Radius Explained

In Blender's Principled BSDF shader, Subsurface Weight controls the overall intensity of the subsurface scattering effect, while Subsurface Radius determines the depth and color distance light travels beneath the surface. Understanding the distinction between these two settings is essential for creating realistic translucent materials like skin, wax, marble, and milk.

Subsurface Weight

Subsurface Weight acts as a blend slider between standard surface shading and subsurface scattering (SSS).

  • Value Range: 0.0 to 1.0.
  • Function: At a value of 0.0, the material behaves as a hard, opaque surface using standard diffuse shading. At 1.0, the subsurface scattering effect is fully active.
  • Primary Use: It dictates how much SSS is applied to the object. Texture maps are often plugged into the Weight input to control which parts of a mesh are opaque and which are translucent.

Subsurface Radius

Subsurface Radius controls the physical behavior of light beneath the surface by defining the average distance light rays travel before bouncing back out.

  • Value Type: RGB Vector (three distinct values corresponding to Red, Green, and Blue light channels).
  • Function: It measures the distance (in Blender units/meters) light scatters per color channel.
  • Primary Use: It dictates how deep light penetrates and which colors bleed through the material. For example, human skin scatters red light deeper than green or blue light because of blood under the surface. Setting a higher value in the Red channel of the Radius vector creates the realistic warm red glow seen on the edges of ears or fingers when lit from behind.

Key Differences

  • Control Type: Weight is a scalar value (single number) that controls blending, while Radius is an RGB vector controlling distance and color distribution.
  • Effect: Weight determines the presence and strength of SSS across the surface. Radius determines the softness, scale, and color tint of the light bleeding beneath the surface.
  • Workflow: You adjust Weight to decide where and how strongly subsurface scattering appears, and you adjust Radius to define the physical material properties like how far light spreads through it.