Perhaps the biggest objection to fiberglass batts in green building circles comes from the binders used to glue the glass fibers into a cohesive mat. These binders usually contain formaldehyde, a chemical known to cause sensitivity in certain people and classified as a human carcinogen by the IARC and as a probable human carcinogen by the EPA.

Most manufacturers insist that the low levels of formaldehyde used in manufacturing fiberglass batts makes any health concern exaggerated when compared to many other building products and naturally occurring off-gassing from raw materials, such as wood. In fact, some fiberglass batt insulation with added formaldehyde has gained Greenguard certification.

But if you are concerned, loose fill or blown fiberglass insulation requires no binder, which means no formaldehyde. For those using batts, Johns Manville offers the only fiberglass batt product line with no added formaldehyde. “We don’t consider the formaldehyde binders in insulation to be a big contributor to indoor air pollution, but since we can use alternatives without formaldehyde, why not do our little part to improve the environment?” explains Erick Olson, a senior technical product specialist for Johns Manville.

Any stuffed insulation requires excellent on-site quality control to perform at its rated R-value. A few missed cuts, gaps, or cracks left between batts, and the R-value plummets. Blown and foamed insulation usually provide a more foolproof system to prevent air infiltration, but an excellent sealing job using a well-aimed caulk gun and a few cans of foam sealant coupled with a craftsmanlike batt installation can yield low-cost insulation results comparable to the blown systems.

Non-Fiberglass Batts

Non-fiberglass batts can be made of cotton, sheep’s wool, or mineral (rock or slag) wool. All of the alternative batt insulation products are made almost entirely from recycled or renewable materials. They offer similar thermal performance as fiberglass but at a slight cost premium. They come unfaced and need the addition of a separate vapor retarder in extreme-cold climate zones.

To make them fire resistant and prevent mold and insect infestation, most alternative batt (and cellulose) insulation fibers are coated with ammonium sulfate or borate. Although one manufacturer advertises its product as so safe a child could eat it, both sulfates and borate are used as pesticides and have toxic properties. At a minimum, a respirator should be worn when installing any kind of insulation.