Insulation helps to protect people inside a building from heat, cold, and noise, and conserves energy. Environmentally preferable insulation options offer additional benefits, such as reduced waste and pollution in manufacture and installation, more efficient resource use, recyclability, enhanced R-value, and reduced or eliminated health risks for installers and occupants. Well-insulated envelopes are cornerstones of sustainable buildings, so consider the following regardless of insulation type:

Insulate as thoroughly as possible to increase comfort, reduce the risk of mold, and save both energy and money for the life of the building. Seek insulation that is free of formaldehyde, including the urea formaldehyde binders commonly used in fiberglass batts. Formaldehyde in the wall cavity is a secondary concern to formaldehyde emitted directly indoors by pressboard furniture and finishes, but the risk of exposure to this carcinogen is unnecessary. The comfort and energy efficiency of your home depend on the R-value of the entire wall, roof, or floor (i.e. “Whole-Wall R-value”), not just the R-value of the insulation. For example, the Oak Ridge National Laboratory has found the whole-wall R-value of 2x6 wood frame walls with R-19 fiberglass batts and paper facer fastened to the inside surface of each stud to be only R-11. Techniques such as Advanced Framing (covered in the structural section of this guide) increase the wall area covered by insulation, increasing whole-wall effectiveness.

Framing conducts far more heat than insulation, much as most window frames conduct more heat than double-paned glass. An additional layer of rigid insulation between framing and sheathing (or insulating sheathing) helps improve whole-wall R-value by insulating the entire wall, not just clear space. In non-“breathable” wall designs, closed-cell rigid foam with taped seams can provide an effective vapor barrier.

Consider alternatives to fiberglass, such as recycled cotton or cellulose (recycled newspaper treated with borate for insect and fire resistance.) Both reduce waste, require one-quarter to one-tenth the energy to produce, and are far less irritating to installer's skin and mucus membranes. See insets for information on several specific types of insulation.

Sprayed polyurethane foams expand to fill cracks, providing both insulation and a vapor barrier. (Sprayed cementitious foams such as Air-Krete have somewhat similar properties.)

If you use fiberglass, use recycled-content products, which save resources and landfill space.

Like all glass products, fiberglass insulation is made primarily from silica heated to high temperatures, requiring significant energy and releasing formaldehyde. Public health threats from glass fibers are well documented, and short term effects include irritation to eyes, nose, throat, lungs, and skin during installation or other contact. Longer term effects are controversial, but OSHA requires fiberglass insulation to carry a cancer warning label. Binders in most fiberglass batts contain toxic formaldehyde that is slowly emitted for months or years after installation, potentially contaminating indoor air.

There are greener options. Recycled cotton insulation insulates as well as fiberglass and offers superior noise reduction. Cotton insulation poses no lung cancer risk and is not irritating during installation. Cellulose insulation also poses no risk of lung disease and offers superior R-value per inch. Both cotton and cellulose are treated with borate, which is not toxic to humans, and makes both materials more resistant to fire and insects than fiberglass.

Finally, recycled-content fiberglass insulation is becoming increasingly available (ask for minimum 25% post-consumer recycled content and minimum 50% total recycled content). Some products are designed with heavier, intertwined glass fibers to reduce airborne fibers and reduce the fraction of fibers that can enter the lungs. Cutting batts to size can limit these benefits, however.

The following websites provide information about products and manufacturers, who can direct you to local retailers: