i found a big bit of plastic in a bin,is there a way of knowing if its uhmw or not?there was plaster board,kitchen cabenets,shop fitting hard wear,also in the bin which makes me think yes.i have never used uhmw so cant compare it.its 20mm thick,the pic has a 12" ruler for scale.it flexes dents and has a waxy slippy feel to it.

It's probably HDPE. UHMW typically does not feel as "waxy" as the lower density materials. About the only way to know with some certainty is to cut a 1" square cube and determine its density.

There are different grades & types of uhmw as well.

thanks

UHMW has always seemed pretty slippery to me. We used it to line the 1 3/4" hose beds on our fire trucks when we switched to rubber coated hose specifically to make it easier to pull the hoses out... the rubber coatings were sticky against the old metal hose bed sides. Either way it will likely work okay for whatever you have in mind though.