I think he may be referring to the heavy vinyl you buy by the yard. It's usually where the roll goods are in the back and are mixed in with the felt backed, vinyl table cloth material. I bought some from my local True Value Hardware store, I got the really thick stuff and will be making sleeves to put around my cased straps. I figure it will keep the moisture content at the right point for me as I work up the strap. I'll just slide the sleeve down as I work.
I never thought of using it for vacuum forming. That puts a whole new slant on things.