**Refraction Model** Specifies the model HDRP uses to process refraction. The options are:
• **None**: No refraction occurs. Select this option to disable refraction.
• **Box**: A box-shaped model where incident light enters through a flat surface and leaves through a flat surface. Select this option for hollow surfaces.
• **Sphere**: A sphere-shaped model that produces a magnifying glass-like effect to refraction. Select this option for solid surfaces.
• **Thin**: A thin box surface type, equivalent to Box with a fixed thickness of 5cm. Select this for thin window-like surfaces.