As commonly available in the stores, these tubes seem to be made of 2
different types of foam, one that is slightly more "rubbery" than the
other. This link says that one is used for copper, the other for
galvanized steel, but it doesn't say which type is for which kind of
pipe: http://frentzandsons.com/content/how...opperpipes.htm

Also, what size should the tube be -- just enough to fit over the pipe,
or slightly larger so that there's some sort of an "air gap" between the
tube and the pipe?

Thank you.