Most cellulose insulation is made from chopped newspaper, treated with fire retardants and has an R-value, or insulation value, of 3.7 per inch, according to Inspectapedia. This material is fluffy, gray to brown and papery in texture. Some cellulose insulation also includes small chips of wood. Cellulose insulation has been used for nearly a century in the U.S. and is considered quite safe as long as the insulation is treated to resist fire. According to Inspectapedia, cellulose insulation is slightly more resistant to mold growth than fiberglass and some other materials.
Fiberglass insulation comes in two forms: the familiar pink batts and a loose fill variety that is blown into walls and attic spaces. Blown fiberglass insulation is pink, yellow, green or white and gets its color from the resin used to stick the glass fibers together. According to the U.S. Department of Energy, fiberglass insulation is often 20 to 30 percent recycled glass. This insulation material does pose some respiratory hazards. Airborne fiberglass particles can damage lungs, and fiberglass insulation that's allowed to become wet may grow hazardous mold. According to Inspectapedia, fiberglass insulation has an R-value of 3.14 per inch.
Rock wool insulation, also called mineral wool and slag wool, is a relatively old material. According to Inspectapedia, rock wool was first developed in the 1850s and patented in the U.S. in 1875. It was commonly used up until the 1950s and still appears in some new construction. According to the U.S. Department of Energy, rock wool insulation contains about 75 percent recycled material from industrial processes. The material looks cottony but is actually made from mineral fiber. Rock wool is white, gray or brownish. The R-value of rock wool varies. Inspectapedia states that it is as low as 2.25 in loose fill installations or as high as R-4 per inch. Rock Wool insulation is relatively heavy and requires a strong support. Its weight makes it less likely to become airborne than fiberglass, reducing the risk of respiratory damage.