TOPIC: Making fiberglass more flexible

I want to push back a section of fiberglass on my boat to repair a crack in the transom - it moves but it very stiff - if you heat up the fiberglass does it become more flexible?

I’ve read on some of the threads, to take the hook out of the bottom of the boat. To use weight and hot water ?
So I guess heat works ?

Are you trying to push fiberglass in, or out ?
Has the fiberglass delaminated from the transom wood ? If so….. you may be doing more work than fixing a crack.
Got any pictures ?

Heat does indeed make fiberglass more flexible, just as it does most plastic. I have used hot water to get hooks out of hulls, and heat guns to allow a slight bit of movement in fiberglass panels. But the movement necessary has been minimal, say 3/4" over a length of perhaps 3 feet or more. Trying to get fiberglass to bend out of the way in a case like you describe may not be wise, or even possible. How much movement do you from the glass? You might look into finding another alternative to access the repair area.