Blocks the movement of air (eliminating the need for a vapor barrier), absorbs sound like a sponge, and flexes with the seasonal movement of the framing. Must be professionally applied. Although not flammable, must be protected from fire with drywall or plaster.
Good for: New construction, or retrofit in attics or crawl spaces
R-value per inch: 4
Vapor barrier needed: No
Cost: 4 times the cost of fiberglass batts.