There was a composite glider, the PIK-20, made in the '70s in a range of colours. I believe it was post-cured/autoclaved so that it wouldn't lose any strength with heat build-up.
I used to have a Std. Libelle and the manual for that said that you should leave it in a matt-painted airtight trailer in full sun on a really hot day to cure some more.
Here's a PIKture:
