Billy, I finally got a chance to pull out the frog I was speaking of and will try to find some time for a photo or two. The front and back has a larger more or less diamond shape set of cross hatchings underneath the rubber. The edges look like a two ply sidewall from a tire or radiator hose if it was made flat instead of curved. Showing the ends of the multiple strands in two layers sandwiched in between the rubber. With the smell rubber like, and if I had to make a guess synthetic? Saying that because some of the period Japanese items I've seen that I believe are natural rubber tend to really deteriorate, whereas that's not the case here. Best Regards, Fred
