Not unusual for the thickness being discussed. No reason to think it isn't UHMW.
I have 3/8 on mine, and I agree with your observation. I don't see it being a willing participant either.
There is a big difference between saving your gel coat by not scraping it off a light boat,
and preventing a piling or a jagged rock from piercing your hull on a big heavy boat.
I've seen 1/4" rolled up, and I've toted 3/8" flat on a trailer. My question if someone knows is,
Will the 5/16" roll up like the quarter inch, or is it like the 3/8 and doesn't want to?
I'm considering 5/16" for the next hull and am curious about this.