TwoSided (Material global keyword)
From modwiki
Description
The twoSided global keyword allows a surface to be viewed from both sides.
Usage
In the global section of your material shader type...
twoSided
Parameters
Not Available.
Notes
By default, polygons will not be rendered at all from the reverse side, which facilitates an important optimisation known as backface culling. However this is incorrect behaviour in some situations, such as when a patch is used to represent a grating or spiderweb, so the twoSided keyword is used in these cases. Using this keyword also implies the noShadows keyword.

