by AndiS » Thu Dec 15, 2016 8:08 pm
If you are so sure, then it make another vague memory of mine more plausible: There were some faces in my life long ago, that happened to be two-sided without any doing by me. That war really long ago and to this day I am not sure whether
a) the plane in question was two-faced in Blender and I did not realise,
b) the material is double-sided (*)
c) it was a default assumption inside Rail Simulator (sic).
(*) I also vaguely remember a check box somewhere for "two-sided material" but that will have been for 3DS Max, in one of Derek's blog posts.
However, in the years gone by, I read so much about all faces needing materials or else the export or loading crashes, that I count my faces carefully. Maybe I should relax on that front. But I am sure I had such nonsense once - a double-sided plane that was textured on one face but not on the other. Nice one if that stop your model from loading. But that has no bearing on your situation since you already delete the outside faces.
Long live the second side of the inside faces as long as you get it for free!