How thick does it have to be? Most rubrails are EPDM rubber (Ethylene Propylene Diene Monomer); I'm considering to order from
technorubberind.com however they don't seem to sell sheets. Their rubrails are specifically made for sib/rib... and cheap... 80ft@ 3" for about $200. A quick google of "EPDM sheet" tells me 1/4" 40sq.ft will cost you about $100... that's in the form of a gym floor mat ... same material; just find the right finish, smooth, glossy, whatever... I'm all for using materials other than their build purpose...