FIBER

Cellulose
Made from shredded, fluffed-up newsprint containing 85 percent recycled material and 15 percent borate-based fire retardant (borates are environmentally safe mineral compounds that also stop mold and pests). Blown in dry or sprayed on wet—damp, really—it has a higher R-value than fiberglass and costs about the same.

Cotton
Ever wonder what happens to old denim? Some of it gets turned into thick batts and is used to insulate walls and floors. Treated with the same borate fire retardant used in cellulose, shredded cotton is a popular low-chemical choice.

Fiberglass
Some might wonder how this material merits mention alongside obviously greener goods, but manufacturers have given spun glass a higher recycled content (up to 40 percent) and have taken steps to reduce the acknowledged problem of airborne fibers. Some makers have started slipping their product inside a bag—a very effective treatment until it has to be cut to fit an odd-size cavity. Comes in batts or is chopped and blown into floor and wall cavities.

Mineral wool
Made from recycled slag and mined basalt rock, mineral wool is naturally resistant to fire and pests and is highly sound absorbent. While it has been associated with the same potential airborne-fiber risk as fiberglass, one mineral wool product, a rigid-board foundation insulation, poses no such problem while providing a waterproof barrier.

Sheep's wool
Sheared from living creatures in the usual way, the cleaned fiber is formed into batts and lofty loose fill, then treated for moth- and mildew-proofing. Like cotton, wool tends to primarily be a health-related choice.
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