Far as I can tell, someone wrote:
I've used it - it's a carbonate cutting material on the paper and the
stuff is amazing when hand sanding. There is a blasting material made
of the same stuff, but I can't remember the name of it.

Carborundum?

It's fantastic.

Paper should be outlawed, as it's a rip off.

Sanding cloth lasts far longer, doesn't tear like paper, doesn't clog
like paper, and is just all around better.

When a place like West Marine sells "marine" sand paper, what they are
doing is proving that they are willing to lie and deceive for a few
bucks.