So this kind of project seems like the easiest for someone to get into MYO gear--any suggestions for patterns and fabric? It seems like it should be as simple as cutting a mummy shape and sewing in a drawstring, but I've also been bag liners that you end up getting tangled up in.

I made one out of thin white silk, and I think it weighed 2 oz or something.

A bag liner can get you all tangled up unless you use safety pins in several places. Even then, you may feel that you need an explosive escape hatch if it gets really bad.

If you are trying to do this to make the bag warmer, then you may be going at this all wrong.

--B.G.--

Most liners seem to be made of silk or a very thin, light fleece I think. I've been trying to find Coolmax material to make one from.

As far as patterns Ive seen a few, just google that. Easiest thing to do would be to lay your fabric over your bag and trace it.