Just found this,
High R Double Sided Foil Insulation: *Out performs R30 fiberglass batt insulation. Preferred over fiberglass blanket insulation in metal buildings. Our most versatile insulaton. Consistent 14.5 R value. Great for all climates. Strong recommedation!
The two layers of reflective foil that surrounds the 1/4- inch closed cell center, forms a radiant heat and vapor barrier.
Key Benefits:
Double-Sided Foil
Vapor Barrier
Radiant Barrier
Class A / Class 1 Fire Rating
Convenient flange tabs on sides
Provides 19 DB Soundproofing
Clean
Lightweight
Very Strong
Saves Money and Energy
http://www.steelbuildingsetc.com/default.asp
A 14.5 R value is very high for 1/4" material, wonder how good it really works?
Spray-in-place polyurethane is good but very expensive.