Insulation Types and MaterialsInstallers recommend a product based on where it’s to be installed, their experience with the product, and their relationships with their suppliers. Here’s a roundup of the most popular types of insulation and materials.

Loose Fill (Blown-in)

For an existing home, loose-fill insulation often makes the most sense in terms of cost, flexibility, and performance. Loose fill is a dry, fluffy material installed by a powered blower. It’s suitable for attics, where installers literally spray it out of a hose and distribute it evenly to the desired depth for a target R-value. It can also be blown into walls through holes created in either the exterior or interior of the wall, between pairs of studs.

Fiberglass fill is manufactured by spinning molten glass into fine glass fibers. There are two kinds of fiberglass fill. “Off-ware” is manufactured using the waste created from producing fiberglass batt insulation; recycled content is typically about 20 to 30 percent. “Virgin” fiberglass is made with no recycled content. Some installers find it easier to work with.

Cellulose fill is manufactured from recycled newsprint, telephone directories, and other wood products. It’s treated with fire-retardant chemicals, usually borates or ammonium sulfate, which have been used safely for decades. Cellulose can also be blown in “wet,” where the fill material is moistened so that it adheres to surfaces and to itself. Wet cellulose insulation seals better than dry insulation, but must be allowed to dry. As a result, it’s best for new construction and remodeling jobs, where it can be left exposed before being walled in.

Mineral wool—spun from minerals like basalt or slag—can also be used for loose fill, but it’s rarely used in the U.S.

Although the differences between fiberglass and cellulose fill aren’t significant in terms of resulting energy efficiency, there are other considerations. Some fiberglass products are treated with formaldehyde, which produces some off-gassing, but it’s at a low enough level that the Environmental Protection Agency and the Consumer Product Safety Commission do not consider it a health hazard. If you’re concerned, request a product that is not treated, and check this on the data sheet, which the contractor must provide.

Another worry about fiberglass is the danger of breathing in fibers. Studies have not established a link between fiberglass and cancer. The American Lung Association’s position is that if it is handled properly it is safe, but working with fiberglass does require precautions to avoid skin contact and inhaling fibers.

Cellulose materials also have some drawbacks. Because cellulose is paper, fire is a concern, although the product is treated with a fire retardant. Since cellulose is more absorbent than fiberglass, moisture is also a concern. Continued exposure to moisture will, over time, degrade insulation materials. Also, moisture will reduce fire resistance by leaching out the retardant.

On the other hand, cellulose tends to fill in and around tight spaces better than fiberglass, resulting in a slightly better seal. In addition, under extremely cold conditions, the R-value of fiberglass is reduced.

One other point: Cellulose materials typically consist of 80 percent recycled material. Fiberglass, at most, is around 30 percent recycled, and it’s recycled from other fiberglass products, which require more energy to manufacture than paper.

Despite the pros and cons of each type of material, the impartial experts we consulted—including DOE researchers and home inspectors—said that fiberglass, cellulose, and virtually all other insulation products work well if installed correctly.

Blanket (Batt and Rolls)

Blanket insulation comes in rolls precut to common stud widths. Batts (typically eight feet long) and rolls (50 feet long) can be purchased with or without a backing, which serves as a vapor barrier. The insulation is installed with the backing toward the living space.

Blanket insulation is used mostly in unfinished attics, in remodeling projects, and in new construction where it can be rolled out between studs. But it’s difficult and labor-intensive to install blanket insulation into hard-to-reach spaces.

Most blanket insulation is made of fiberglass, but mineral wool is also available. Two other materials are cotton (made from shredded, recycled denim) and sheep’s wool. These options are considerably harder to find and more expensive.

Spray-in Foam

Spray-in foam provides a greater R-value for a given thickness, which makes it useful where space is limited. Installers mix and spray the material into place. It expands and stiffens, and can be installed in closed wall spaces or in open cavities during remodeling or new construction.

But foam costs two to five times more than fiberglass or cellulose insulation. And if improperly installed in existing walls, it can expand too much, pushing against drywall, creating gaps or causing new cracks.

Urea-formaldehyde foam insulation (UFFI) was banned by the Consumer Product Safety Commission in 1982 after years of problems, including concerns about formaldehyde off-gassing. Safer plastic products—and, recently, a soy-based product—have replaced UFFI.

Insulating Foam Board

Foam insulation panels—the kind used as sheathing on roofs and stud walls on homes under construction—are typically used in new construction or as part of a major remodeling job. There are several types, all of which offer the advantage of high R-value per inch (from R-4 to R-8). Foam insulation panels are good alternatives when there is open access to the area to be insulated, and insulating space is at a premium.