How can I set a plane’s normals facing both sides?
I’m assuming your having an issue in a game engine? Unfortunately that’s not possible. You’ll most likely need to duplicate the object and reverse it’s normals, if you don’t have any restrictions against something like that. Hope that helps. If that’s not the case, more info is needed to help you solve the problem. What is it your specifically trying to do?
Normals cannot face both sides, by definition. A two-sided shader however will use this to apply different materials based on the normals, and those materials may be identical, causing the object to render as though the normals faced both ways. That is also true in realtime engines.
I rendered a plane mesh which seems from both sides.
Under the Material , check "Both Sides " and it should render front and back in the engine.