I'm replacing the wall insulation in a free-standing one-room building
built in 1977. The studs are 13 inches apart, and the original
Kraft-batted fiberglass insulation is 13 inches wide. Can you still buy
13-inch wide fiberglass insulation anywhere?

And what about some of the other insulation options available, such as
polystyrene and Reflectrix -- are those worth looking into? Does
Reflectrix work on its own, or only in addition to something like
fiberglass?

Thanks!