Mike W. wrote:
. . . Now I buy foam without the skin. . .
Not sure why you would buy foam with the skin on in the first place. Rare times I've bought small chunks from our canoe dealer, and I've never been offered pieces with skin on. Nor would I accept them if they were offered.
More often, I've bought foam by the complete sheet ('bun') from the supplier, and they cut the skins off, as well as slice the foam into various thicknesses, for no extra charge.
I take the skins, usually around 1/8" thick, and glue them onto high-wear areas (knee blocks, saddles) with the shiny side out, to prevent the usual wear-and-tear of the foam. Waste not, . . .