I used the insulation from the local hardware store. It's the stuff that looks like 1/2" thick bubble wrap with foil on both sides. Bought a 6" x 20' roll. It worked out to be just enough to do the roof of the cab; got a couple of feet left over.
I did one 6" strip at a time. Cut to fit then spray with super 77 adhesive and stick it on. Repeat until roof is done.
