Probably you read this post by RichHI stand corrected. It is nylon.
"For small repair jobs, go to a drugstore and find Dental Floss made by W.L.Gore. This is similar to the Super high tech "Tenara" PTFE thread (also by W.L.Gore the maker of 'Goretex').
Both are used with a #16 needle on a sewing machine. "