plastic-coated foam board

This is not really about printers or printing, but what are you gonna do with those prints but mount them?

Anyway, I recently got some 3/16" foam core from a local frame shop and thought it felt a little weird... maybe a little heavier than I'm used to. When I tried to cut it, it was resistant to the cutter, so I pushed a little harder and it cut okay but I noticed that on the cut-off piece, the "paper" backing was in little broken sections! It looks for all the world like plastic, which I've never seen before. Has anyone ever seen this?
Thanks