No 20 mil is right...
http://www.teamfitzgraphics.com/helmet-decals/football-helmet-decals.html
Made with a thick and durable 20-mil. vinyl, these Football Helmet Decals will last the rigors of an entire season. They arrive ready to peel and apply and conform to the complex curves of your helmets with ease.
^check out that site...says that on it.
anyone else might know?