2 mm thick sturdy plastic. I probably should have gotten the one for medium pile carpet. Maybe it won't indent as much where the wheels of my chair presses down on it. But the short pile one was cheaper so I got that one instead. Will see how long it lasts before these indentations turn into cracks. It was able to unroll and flatten itself in 24 hours in room temperature. Didnt like how the tape used to roll it up for shipping left a sticky residue though. Made in USA.