Okay guys, I've been following this debate on Game Bag materials, etc. and gave it some thought. I have been using pillow cases as well, as I thought the cheese cloth bags were next to worthless. I checked out some of the commercial synthetic game bags for sale, and see they are approximately $50.00 for 6 big bags. I also read that they should breathe, and do a "blow through them" test to see about that.
Today, I was in Walmart and checked out some fabric with my wife. They had a polypropylene fabric that was pretty tightly woven, and yet you could blow through it, proving it breathes. I don't think a fly could lay eggs through it either. It was $1.49/yard. We bought 6 yards of it for under $9.00. Wifey is going to custom sew me some game bags from it. It weighs far less than 6 cotton pillow cases, even before it's been cut up and the excess discarded. I think it will compress somewhat in a pack too.
So, I'm excited to see if this material does the trick? If not, I'm out the same amt. of money I could have spent on a 12 pack!