It is polyethylene. I did order 10' each of 1/4", 3/8", 5/8", and 3/4" from another place for $5.78, plus $4 shipping, but the temp rating of what I ordered is only 220 degrees F. Also polyethylene, so probably the same temp. I guess I'll put a piece in my engine bay, and go for a drive. If it melts, wrong stuff. I just wish I could see what it looks like.