The Mtl 2 Sided Material is a utility material provided with the V-Ray renderer. The material allows the light to be seen on the backside of objects.

Use this material to simulate thin translucent surfaces like paper, cloth curtains, tree leaves, etc.

This section lists input sockets that are not found in the Properties tab but only as inputs for the node.

Front – The material that is used for the front-side faces as defined by the object normals.

Back – The material V-Ray uses for the back side faces as defined by their normals.

Translucency – Determines which side (front or back) relative to the camera is more visible in the rendering process. By default, this value is 0.5, which means that both the side facing the camera and the one facing away from it are visible to the same degree. When this parameter is closer to 0.0 more of the material facing the camera is going to be seen. When it is closer to 1.0, more of the back material is seen. A color node can be connected to control this parameter. 

Translucency Strength – A multiplier for the Translucency parameter.

Force Single-sided Sub-materials – When enabled (the default), the sub-materials render as one-sided materials. Turning this option off is not recommended.

Multiply By Front Diffuse – When enabled, the translucency is multiplied by the diffuse of the front material.