I just checked with B & B Distributors, LLC and John Smith advised that
all of his headphones (so that would include the
Killer B Wasp Optima model.) have
leather muffs.
According to the B & B Distributors ad on the Internet, vinyl muffs have a life expectancy of (3) years and then the material begins to harden, showing cracks, tears and dents (vinyl memory) and some of it's ambient noise blocking ability is lost.
I'm using one of Rick Viola's headphones from his very first production run (last name may not be spelled correct...going on memory.

). I believe he called them Rat phones
Max. Not sure if the muffs are vinyl or some other man-made material, but the material did crack, even though I regularly wiped it off with a warm/damp paper towel and dried after every use for the first few years. I tried to make contact with him at that time, to see if he would replace the muffs, but his website had gone off the Internet !
I'm still using my Rat phones
Max headphones with the cracked muff material. Due to failing health, I don't get out to hunt much, so making do. However, I'm thinking about buying Killer B Wasp Optima's when funds are available. Sorry I didn't buy those in the first place !
ToddB64