I have some prepreg that is close to a year old. I have used it in my AutoClave and it seems to have cured OK. But has it really.
Could anyone tell me the signs to look for in prepreg when its no longer good. It didn't seem to be as sticky to the touch as it was when fresh. Any information would be appreciated.
Fred

When it feels like cardboard? Haha. If it cures and isn't brittle then it's fine, at least for non-structural applications. If you're building an aircraft or a formula 1 car then it's no good past its use-by, but if you're making a wing mirror cover then it's absolutely fine as long as it cures. 

Pre pregs can feel stiff if they have been out of the freezer for too long but they can still be perfectly ok.

I test a sample simply by flashing some heat from a hair dryer on it and if it become tackier then it will certainly flow at the higher cooking temp. If it does not become any tackier then it's no good.

Thanks for your reply.
I guess that if the resin it starts to flow with heat from a heat gun, then it has not cross linked.
Fred 

make a test panel, see how it reacts.  Send off a sample to a lab and have it tested. For aerospace this is required.  The lab, usually the manufactuer's, will then give a re certification for 3-6 months.