Here's the handout for the class I used to do on gamebesons
I think one of the most important things about gambesons is to make
them out of natural fiber. It makes a huge different in the comfort and
heat retention level.
Pre-quilted fabric is okay if both the padding and the cover fabric are
cotton. Run away from polyester!
It has occured to me that some of the new high tech might be usable for
the inside layer but I wouldn't know where to get them by the yard.