Lightweight batts of spun glass offer a predictable R-value if not compressed, but the fibers offer little resistance to air movement and convective heat loss. The sample shown is held together with a nontoxic acrylic binder instead of the typical formaldehyde-based binder.
Good for: New construction, attics
R-value per inch: 3-4
Vapor barrier needed: Yes
Cost: 38¢ per sq. ft.