Think back to the quilts of old (crazy quilts)- they used whatever fabrics that were available and it worked out fine! Depending on the fabrics, you may have to adjust a bit, but use whatever you want. If the flag is very thin or you use a t-shirt, simply interface them. Also, quilts that I have made for my hunter/fishermen that I know will be in the truck, on the boat and generally well used, I tend to do a bit of extra stitching to go along with the extra use!