How to Use the Hair Info Node in Blender Shaders

The Hair Info node in Blender is a specialized shader node designed to extract data from hair strands and curve particles, allowing for advanced material customization. This guide explains how to locate the Hair Info node, breaks down the function of each output socket, and demonstrates practical ways to use it alongside the Principled Hair BSDF and other shaders to create realistic hair, fur, and carpet materials.

How to Add the Hair Info Node

  1. Select the object containing your hair particle system or curve strands.
  2. Open the Shader Editor workspace.
  3. Ensure the render engine is set to Cycles or EEVEE (note: some outputs are optimized for Cycles).
  4. Press Shift + A in the Shader Editor to open the Add menu.
  5. Navigate to Input > Hair Info (or search for "Hair Info").
  6. Click to place the node in your node tree.

Understanding the Hair Info Outputs

The Hair Info node provides specific data per strand, root-to-tip point, or hair system:

  • Is Strand: Outputs a value of 1.0 for hair geometry and 0.0 for regular surface geometry. Use this as a factor in a Mix Shader node to apply different materials to the scalp and the hair strands.
  • Intercept: Outputs a gradient value from 0.0 at the root of the strand to 1.0 at the tip. This is the most common output used for driving color changes along the length of the hair.
  • Length: Outputs the absolute length of each individual hair strand in Blender units. This allows you to alter properties like color or roughness based on how long a hair strand is.
  • Thickness: Outputs the thickness/width of the hair strand at any given point along its length.
  • Tangent: Outputs the direction vector along the strand. This is typically plugged into the Tangent input of an Anisotropic BSDF node to create realistic light reflection along the direction of the hair fibers.
  • Random: Outputs a unique random value between 0.0 and 1.0 for every individual hair strand. This is ideal for breaking up uniform colors by injecting subtle variations across the entire hair system.

Practical Usage Examples

1. Creating a Root-to-Tip Color Gradient

To make hair roots darker than the tips:

  1. Connect the Intercept output of the Hair Info node to the Factor input of a Color Ramp node.
  2. Set the left handle of the Color Ramp to a dark color (for the root) and the right handle to a lighter color (for the tip).
  3. Connect the Color output of the Color Ramp to the Base Color of a Principled BSDF or Color input of a Principled Hair BSDF.

2. Adding Random Strand Variation

To make a hair system look natural by giving individual strands slightly different colors:

  1. Connect the Random output of the Hair Info node to the Factor input of a Color Ramp node.
  2. Define two or three subtle variations of your target hair color in the Color Ramp handles.
  3. Connect the Color Ramp output to your shader's color input.

3. Masking Surface vs. Hair

If your emitting surface shares the same material slot as your hair particle system:

  1. Connect the Is Strand output to the Factor of a Mix Shader node.
  2. Plug your surface shader (e.g., skin/scalp material) into the top Shader input.
  3. Plug your hair shader into the bottom Shader input.