It is glass from GPSW. When I first installed it, I had trouble with the carbs seemingly getting dirty. The bike would sit for several weeks and after running it, shutting off, and starting a few weeks later, run like crap/. Clean carbs and all was good. This happened several times. All with same fuel source, that I still use. A Shell in Edgerton Wi that is on my way home when I go to the Northwoods snowmobiling. Closest place to me with non ethanol premium. . After the last cleaning last summer things have been fine. I do start slightly more often, but she purr's. I may have had some bad gas at first not sure. Nothing ever showed in carbs. I installed the tank as sent, maybe it had some residue in it.So far so good. I keep non ethanol premium in it , refill from a 5 gal can, with Gas RX additive. I filled that can last in March and added the Gas RX then. I don't see any failure of the tank, and it has been full since I bought it in August 2012, summer heat and in cold storage.