What Kind of Insulation in the Attic Is the Brown Insulation?

Nichole Fox

Insulation comes in a variety of colors. Brown insulation is made up of mineral wool, which comes from either rock -- natural materials -- or slag -- the scum on the surface of molten metal. The U.S. Department Of Energy notes that 75 percent of mineral wool is derived from post-industrial content.

Brown insulation is available in either blanket, rigid foam board or loose-fill form.


The Federal Trade Commission determines the R-value standard. The R-value indicates thermal resistance and is affected by the type of material, thickness and density. The greater the R-value, the more effective the insulation is. R-value recommendations from the U.S. Department Of Energy (DOE) are based on climate. Combining insulation can increase R-values. Insulation compression can lower the effective R-value of insulation. To find recommendations for R-values in your area, access the DOE website for its R-value data.

Rock Wool

The R-values of rock wool range from 2.8 to 3.7 per inch. This product has a higher density than cellulose and foam, making it a smart choice for wall cavities and attics. Rock wool does not contain asbestos or use CFC gases in its production. It is an eco-friendly choice because it is mostly derived from post-industrial materials. While the binding agent used in its production is the carcinogen, phenol-urea-formaldehyde, the finished product does not contain free formaldehyde.


Fiberglass (glass wool) is a common form of insulation made up of needle-like threads of glass. Fiberglass comes in blankets or loose-fill. To insulate limited cavities, fiberglass technology has evolved to include higher-density varieties. The DOE estimates glass in fiberglass ranges from 20 to 30 percent post-consumer content. The American Lung Association recommends goggles, gloves and a dust mask, when working with fiberglass, to prevent fibers from entering the lungs. Fiberglass fibers can inflame lungs, causing respiratory issues.


Vermiculite was a popular insulation choice between 1919 and 1990. An asbestos-contaminated mine in Libby, Montana supplied over 70 percent of the vermiculite used in insulation products. The Illinois Department of Health notes that disturbed asbestos produces tiny needle-like fibers that can cause irreparable lung damage. Do not disturb vermiculite insulation; call an asbestos-certified professional for assistance. The Environmental Protection Agency provides ways to identify vermiculite on its website, generally a pebble-like material, typically gray-brown or silver in color.