Types of Insulation

Types of Insulation

Rigid Fiber Board Insulation

Rigid fiber or fibrous board insulation consists of either fiberglass or mineral wool and is primarily used for insulating air ducts in homes. It is also used when there's a need for insulation that can withstand high temperatures.

Fiber or fibrous glass duct board insulation is manufactured from resin-bonded, inorganic glass fibers. These duct boards are available with coated or faced airstream surfaces. The outside surface of the boards typically incorporates a factory-applied reinforced aluminum air barrier and water vapor retarder. They come in a range of thicknesses from 1 inch to 2.5 inches. The boards can provide an R-value of about R-4.0 per inch of thickness.


The installation of fiber board insulation in air ducts usually requires an HVAC contractor.

HVAC contractors fabricate fiber board insulation into ducts either at their shops or at the job sites.

On exterior duct surfaces, they can install the insulation by impaling it on weld pins and securing with speed clips or washers. They can also use special weld pins with integral-cupped head washers. Unfaced boards can then be finished with reinforced insulating cement, canvas, or weatherproof mastic.

Faced boards can be installed in the same way. Joints between boards are sealed with pressure-sensitive tape or glass fabric and mastic.

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 can be used in two different insulation forms: blanket (batts and rolls) and loose-fill.

A Canadian company produces a softer, batt-type mineral product. This product is denser, fits standard wall cavities tighter, and is somewhat less prone to air convection thermal losses than standard fiberglass batt products. Its thermal resistance is approximately R-3.7 per inch, which is comparable with sprayed cellulose insulation or high-density fiberglass batts.

Cellulose Insulation Material

Cellulose—a material used as loose-fill insulation—is made from recycled wood fiber, primarily newsprint. The wood fiber is shredded and pulverized into small, fibrous particles that pack tightly into closed building cavities, inhibiting airflow. This provides a thermal resistance of R-3.6 to R-3.8 per inch.

Manufacturers add chemicals to the cellulose to make it insect and fire resistant. The major disadvantage of cellulose is that it absorbs more water than fiberglass or mineral wool. This can become a problem if water leaks from the outdoors since cellulose wicks water into itself and stores it. Too much water can also wash away the fire retardant.

Fiberglass Insulation Material

Fiberglass (or fiber glass)—which consists of extremely fine glass fibers—is one of the most commonly used insulation materials. It's used in two different insulation forms: blanket (batts and rolls) and loose-fill.

Fiberglass Blanket (Batts and Rolls) Insulation

Manufacturers now produce medium- and high-density fiberglass batt insulation products that have slightly higher R-values than previous varieties. The denser products are intended for insulating areas with limited cavity space, such as cathedral ceilings.

High-density fiberglass batts for a 2 × 4 inch (51 × 102 millimeter [mm]) stud-framed wall has an R-15 value, compared to R-11 for "low density" types. A medium-density batt offers R-13 for the same space. High-density batts for a 2 × 6 inch (51 × 152 mm) frame wall offer R-21. High-density batts for an 8.5 inch (216 mm) spaces offer about an R-30 value. R-38 for 12 inch (304 mm) spaces is also available.

One unconventional fibrous insulation product combines two types of glass, which are fused together. As the two materials cool during manufacturing, they form random curls of material. This material is less irritating and possibly safer to work with. It also requires no chemical binder to hold the batts together, and the material even comes in a perforated plastic sleeve to assist in handling.

Fiberglass Loose-Fill Insulation

Fiberglass loose-fill insulation is made from molten glass that is spun or blown into fibers. Most manufacturers use 20%–30% recycled glass content. Loose-fill insulation must be applied using an insulation blowing machine; it is designed for open-blow applications (such as attic spaces) or closed-cavity applications (such as those found inside walls or covered attic floors).

One variation of fiberglass loose-fill insulation is the Blown-In-Blanket (BIB). The BIB is similar to the more common "wet-spray" cellulose in that the material is mixed with a latex adhesive, misted with water to activate the glue, and blown into wall stud cavities. Tests have shown that walls insulated with a BIB system are significantly better filled than those with other forms of fiberglass insulation, such as batts.

U.S. Department of Energy - Energy Efficiency and Renewable Energy