The R-value of an insulation depends on its thickness, density and composition. Insulation found in homes can be made of fiberglass, rock wool and cellulose. Fiberglass is just that, threads of glass. It is spun from molten glass and often contains 20 percent to 30 percent recycled glass. Fiberglass insulation is usually pink or white.
Rock wool has a texture similar to fiberglass' but is a dark gray.
It is spun from blast-furnace slag. A lot of older buildings have rock wool. Today fiberglass and cellulose are used in our area. Fiberglass and rock wool do not require treatment. When installed properly, the R-value per inch of fiberglass is 2.2 to 2.7, rock wool 3 to 3.3 and cellulose 3.2 to 3.8, we learned from the U.S. Department of Energy.