i think once it reaches a certain temp it reaches a point and then once its cooled it doesent strech as much, this is what ive been told anyway.
tazzy, it could get really hot and shrink again, but not sure, and tbh you wouldnt have to strech it loads on a bonet, and youde proberbly tuck some underneeth the bonet so if it did shrink youde have a little leeway