But, then it just doesn't look the same and almost never replicates the aircraft we're trying to model. Last but not least, none of the plastics coverings provide the strength needed on today's larger models. The second benefit of fabric on a wing is it provides a monocoque construction. Now try Poly-Fiber and that strength will more than double and it will stay put. Poly-Fiber been used on aircraft for more than 30 years and we will try to explain a few tricks.
Polyester has a memory when it is woven and that is why it shrinks when heated.
It is returning to its original position. That is where we get confused. It depends on the fabric, the weave, the manufacturer, and last but certainly not least, the temperature at which we shrink. It does an excellent job of temperature control. This way the Poly-Tak won't soak into the wood and the grain positively won't show through the fabric.