Builders have been stuffing homes and businesses with fiberglass insulation for years because it's fairly easy to manufacture and works well. It consists of a fine matrix of flexible glass fibers that creates thousands of microscopic cells. These tiny pockets trap air and keep it from circulating, which reduces convection and heat transfer. However, the small glass fibers can stick into the skin and cause irritation. They can also get into the eyes and into the lungs if inhaled. Some reports, such as the 1994 Annual Report on Carcinogens, have labeled fiberglass as "possibly carcinogenic," prompting manufacturers to apply related warnings to their products.
Denim insulation carries no such warnings. It doesn't cause itching or irritation and can be installed without gloves, safety goggles or a dust mask (although DIY types and professionals may still want to wear a mask while cutting the batting). And it's safe for the long haul. Unlike some materials that off-gas toxic vapors or volatile organic compounds as they sit in your home, denim insulation sits inertly in your walls and floors, blocking the flow of heat without releasing harmful chemicals or irritants.
But does it work? Does it actually compete with the pink fiberglass made famous by the cartoon panther of the same color? Let's do a head-to-head comparison of the three most important functional attributes of building insulation -- R-value, acoustic performance and fire resistance.
R-value measures an insulation's resistance to heat flow. If a material has a high R-value, it has a greater insulating effect. Fiberglass batting with a thickness of 3.5 inches (8.9 centimeters) delivers an R-value of 10.90 [source: Nave]. Increase the thickness to 6 inches (15 centimeters), and the R-value of fiberglass soars to 18.80 [source: Nave]. The same thicknesses of denim insulation deliver R-values of 13 and 21, respectively [source: Bonded Logic ]. Score one for denim.
See how denim insulation fares on acoustics and fire resistance next.