Actually they test a paper plane to a tunnel and they suppose that this special paper will stand the heat generated by friction.
The most critical thing while returning from the outer space is when the plane goes into the atmosphere with some 3 or 3.5 degrees (less will bounce, more will collide) and the temperature at the edges of it;s wings climb more than 3000 Cecilius. Imagine the thermal fatiguing of this thing!
