Neoprene Rubber Sheet 5mm Thick 20cm x 30cm

It's just over 5mm thick and otherwise just as expected, but it curves up at the edges and no amount of leaving it for extended periods of time, rolled back on itself or under heavy weights, will make it lie flat. Even soaked in hot water first.It turns out, when the stuff is manufactured, the big sheet is rolled straight up while it's still hot, ready for transportation, so it cools on the roll and retains that shape. I guess it would cost a bit more if it were allowed time to cool before rolling it up.Obviously, if it's stuck to a flat surface, or clamped between two flat services, you're not going to notice and the seller insists that this is the norm when supplied for gasket making. But there are lots of possible uses for the stuff and I was hoping for a flat piece; they're certainly made to look flat in the picture.Incidentally, no glue I can find will effectively stick to it. Epoxy resin glue will just about hold, but not under any strain.

NO WORRIES, AS DESCRIBED