Insulation materials run the gamut from bulky fiber materials such as fiberglass, rock and slag wool, cellulose, and natural fibers to rigid foam boards. Bulky materials resist conductive heat flow in a building cavity. Rigid foam boards trap air or another gas to resist conductive heat flow. Other less common materials included cementitious and phenolic foams, vermiculite, and perlite.
Fiberglass, consisting of extremely fine glass fibers, is one of the most ubiquitous insulation materials. It’s commonly used in two different types of insulation: blanket (batts and rolls) and loose-fill and is also available as rigid boards and duct insulation. High-density fiberglass batts for a 2 by 4 inch stud wall have an R-15 value. High-density batts for a 2 by 6 inch frame wall offer R-21, and high-density batts for an 8.5-inch spaces yield about an R-30 value.
One newcomer on the fibrous insulation market combines two types of glass which are fused together. As the two materials cool during manufacturing, they form random curls of material, thus requiring no chemical binder to hold the batts together. This eliminates the toxicity of chemical binders e.g. formaldehyde used in other fiberglass products. In more that trace amounts, formaldehyde has been implicated with various health concerns.
Mineral Wool Insulation Materials
The term “mineral wool” typically refers to two types of insulation material:
• Rock wool, a man-made material consisting of natural minerals like basalt or diabase.
• Slag wool, a man-made material from blast furnace slag (the scum that forms on the surface of molten metal).
Mineral wool contains an average of 75% post-industrial recycled content. It doesn’t require additional chemicals to make it fire resistant, and it is commonly available as blanket (batts and rolls) and loose-fill insulation.
Cellulose Insulation Material
Cellulose insulation is made from recycled paper products, primarily newsprint, and has a very high recycled material content, generally 82% to 85%. The paper is first reduced to small pieces and then fiberized, creating a product that packs tightly into building cavities, inhibits airflow, and provides an R-value of 3.6 to 3.8 per inch.
Manufacturers add the mineral borate, sometimes blended with the less costly ammonium sulfate, to ensure fire and insect resistance. Cellulose insulation typically requires no moisture barrier and, when installed at proper densities, cannot settle within the building cavity.
Natural Fiber Insulation
Some natural fibers — including cotton, sheep’s wool, straw, and hemp — are used as insulation materials.
Cotton insulation consists of 85% recycled cotton and 15% plastic fibers that have been treated with borate — the same flame retardant and insect/rodent repellent used in cellulose insulation. One product uses recycled blue jean manufacturing trim waste. As a result of its recycled content, this product uses minimal energy to manufacture. Cotton insulation is available in batts with an R-value of R-3.4 per inch. Cotton insulation is also nontoxic, and you can install it without using respiratory or skin exposure protection. However, cotton insulation costs about 15% to 20% more than fiberglass batt insulation.
For use as insulation, sheep’s wool is also treated with borate to resist pests, fire, and mold. It can hold large quantities of water, which is an advantage for use in some walls, but repeated wetting and drying can leach out the borate. The thermal resistance or R-value of sheep’s wool batts is about R-3.5 per inch, similar to other fibrous insulation types.
Straw bale construction, popular 150 years ago on the Great Plains of the United States, has received renewed interest. Straw bales tested by Oak Ridge National Laboratory yielded R-values of R-2.4 to R-3.0 per inch. But at least one straw bale expert claims R-2.4 per inch is more representative of typical straw bale construction due to the many gaps between the stacked bales.
Hemp insulation is relatively unknown and not yet commonly used in the United States. Its R-value (about R-3.5 per inch of thickness) is similar to other fibrous insulation types.
Polystyrene, a colorless, transparent thermoplastic, is commonly used to make foam board or beadboard insulation, concrete block insulation, and a type of loose-fill insulation consisting of small beads of polystyrene. The thermal resistance or R-value of polystyrene foam board depends on its density, and ranges from R-3.8 to R-5.0 per inch. Polystyrene loose-fill or bead insulation typically has a lower R-value, around R-2.3 per inch, as compared to the foam board.
Polyisocyanurate or polyiso is a thermosetting type of plastic, closed-cell foam that contains a low-conductivity, hydrochlorofluorocarbon-free gas in its cells. The high thermal resistance of the gas gives polyisocyanurate insulation an R-value ranging from R-5.6 to R-8 per inch. Over time, the R-value of polyisocyanurate insulation can drop as some of the gas escapes and air replaces it, a phenomenon known as thermal drift. Data indicates that most thermal drift occurs within the first two years after the insulation material is manufactured. For example, if the insulation has an initial R-value of R-9 per inch, it will likely drop to R-7 per inch, then remain unchanged unless the foam is damaged.
Polyurethane is a foam insulation material that contains a low-conductivity gas in its cells. The high thermal resistance of the gas gives polyurethane insulation materials an R-value ranging from R-5.5 to R-6.5 per inch. Like polyiso foam, the R-value of closed-cell polyurethane insulation can drop over time as some of the low-conductivity gas escapes and air replaces it. Most this thermal drift occurs within the first two years after the insulation material is manufactured, after which the R-value remains unchanged unless the foam is damaged.
Soy-based, polyurethane liquid spray-foam products are also available. The cured R-value is about R-3.5 per inch.
Vermiculite and Perlite Insulation
Vermiculite and perlite insulation materials are commonly found as attic insulation in homes built before 1950. Vermiculite insulation materials aren’t widely used today because they sometimes contain asbestos. However, according to the U.S. Environmental Protection Agency, asbestos is not intrinsic to vermiculite. Only a few sources of vermiculite have been found to contain more than tiny trace amounts.
Vermiculite and perlite consist of very small, lightweight pellets, which are made by heating rock pellets until they pop. This creates a type of loose-fill insulation with a thermal resistance of up to R-2.4 per inch. These pellets can be poured into place or mixed with cement to create a lightweight, less heat-conductive concrete.
Urea-Formaldehyde Foam Insulation
Urea-formaldehyde (UF) foam was used in homes during the 1970s and early 1980s. However, after many health-related court cases due to improper installations, UF foam is no longer available for residential use and has been discredited for its formaldehyde emissions and shrinkage.
Cementitious Foam Insulation
Cementitious insulation material is a cement-based foam used as sprayed-foam or foamed-in-placed insulation. One type of cementitious spray foam insulation known as aircrete contains magnesium silicate and has an R-value of about 3.9 per inch. With an initial consistency similar to shaving cream, aircrete is pumped into closed cavities. Cementitious foam costs about as much as polyurethane foam, is nontoxic and nonflammable, and is made from minerals (like magnesium oxide) extracted from seawater.
Phenolic Foam Insulation
Phenolic (phenol-formaldehyde) foam was somewhat popular years ago as rigid foam board insulation. It is currently available only as a foamed-in-place insulation. Phenolic foamed-in-place insulation has a R-4.8 value per inch of thickness and uses air as the foaming agent. Major disadvantages of phenolic foam are that it can shrink up to 2% after curing, and that it out-gasses formaldehyde. In more that trace amounts formaldehyde has been implicated with various health concerns.