What Is Index of Refraction (IOR) in Blender?

The Index of Refraction (IOR) in Blender is a material property that determines how light bends when passing through a surface, as well as how reflective that surface is at different angles. Controlling IOR is essential for creating realistic transparent and semi-transparent materials like glass, water, ice, and gemstones. This article explains what IOR represents, how Blender uses it in shaders like the Principled BSDF, and provides common IOR values to help you achieve physically accurate 3D renders.

How Light Bending Works in 3D Rendering

In physics, the Index of Refraction measures how much light slows down and changes direction when entering a material from a vacuum or air. In Blender, this calculation dictates two main visual behaviors:

  1. Refraction: The bending and distortion of light passing through a transparent object.
  2. Reflection (Fresnel Effect): How reflective an object appears depending on the angle from which you view it.

An IOR value of 1.000 means light travels straight through an object without bending or reflecting, rendering the object completely invisible. Values above 1.000 bend light more sharply, producing stronger visual distortion and increasing surface reflectivity.

Using IOR in Blender Nodes

Blender uses IOR across several core shaders inside the Shader Editor:

  • Principled BSDF: Controls both refraction (when the Transmission value is above 0) and the Fresnel reflection curve. The default value is set to 1.450.
  • Glass BSDF: Uses IOR to simultaneously simulate light reflection and refraction through a medium.
  • Refraction BSDF: Uses IOR strictly to bend transmitted light without adding specular highlights or reflections.

Common Real-World IOR Values

To maintain physical accuracy in your scenes, set Blender's IOR values to match real-world measurements:

  • Air: 1.000
  • Ice: 1.309
  • Water: 1.333
  • Clear Plastic / Acrylic: 1.490
  • Standard Crown Glass: 1.520
  • Flint Glass (Heavy): 1.620
  • Diamond: 2.417

IOR in Opaque Materials

IOR is not limited to glass or liquids. Even on completely opaque surfaces, IOR dictates specular reflectivity via the Fresnel effect. Looking directly at a surface shows its baseline reflection, while viewing it from a grazing angle increases reflectivity toward 100%. Adjusting IOR on non-transmissive surfaces changes how prominent these edge reflections appear.

Tips for Getting Accurate Refraction Results

  • Check Mesh Normals: Blender uses the orientation of face normals to determine whether light is entering or exiting a mesh. If normals point inside out, refraction will calculate incorrectly and make glass look solid or black.
  • Ensure Surface Thickness: Refraction relies on light entering and exiting a volume. Single-sided planes with high IOR values distort light endlessly; use actual mesh volume or a Solidify modifier for glass objects.