It's thick leather and it's the leather is butted together on one side and stitched together so the raw part of the leather is in the inside. They are very sturdy. The bottom has an extra piece inserted so the bottom of the ProVari doesn't go all the way to the bottom. The bottom is opened so it's really a tube.
Thanks Susan!
Maybe in the Saloon so as not to be taking over Shellro's thread, but I'd appreciate it if someone could post a pic of the bottom. I found a piece of really pretty blue dyed leather and was thinking of making my own sleeve out of it. There should be plenty to play with.