Software:
Unreal Engine 4.24
The TeoSidedSign node let’s the shader “know” if a rendered polygon is facing the camera or not by outputting a value of 1 for facing polys and -1 for back-facing polys.
This is useful for creating materials that have different properties when seen front-facing or back-facing.
Example 1:
Blending two different colors based on face direction:
- Check the Two Sided material attribute.
* Needed so that the engine will render the polygons beck sides.
- In the material blueprint, create a blend of to colors using a Lerp (LinearInterpolate) node and connect it to the material’s Base Color input.
- Add a TwoSidedSign node to get polygon facing input (1,-1).
- Connect the TwoSidedSign node’s output to a Clamp node to clamp the values to (1,0).
- Connect the Clamp node’s output to the Lerp node’s Alpha input so that the polygon’s facing direction will control the Lerp blend.
Note:
You can use this method to blend any other material attribute based on polygon facing direction.

Example 2:
Create an “inwards facing” flipped normal material:
- Set the material’s Blend Mode to Masked.
* Needed for being able to make areas parts of the mesh invisible.
- Check the Two Sided material attribute.
* Needed so that the engine will render the polygons beck sides.
- Add a TwoSidedSign node to get polygon facing input (1,-1).
- Connect the TwoSidedSign node’s output to a Clamp node to clamp the values to (1,0).
- Connect the Clamp node’s output to a 1-X node to invert the facing input.
- Connect the 1-X node’s output to the material’s Opacity Mask input so that polygons facing the camera will be invisible.

Related:
- Blending material using Paint
- Material Functions
- UE4 Bump Map