identifying plastics


I've been trying to build a poly cap but im having trouble finding the
plastic, it is not sold here in Mexico. The closest I've found is a clear
plastic that is very thick and is sold in
almost every big supermarket. 

I was wondering if anyone on the list is could help me identify if this is
poly plastic and the thickness of it ???

Im trying to build a 1000w TC system, I was going to build glass caps but
they seem to be not a very good option.

Thanks all for your help.

Jorge F.