Difference Between Glass & Rock Wool

Composition

• Rock wool is called a mineral wool because it is made primarily from basalt, an igneous rock, according to the North American Insulation Manufacturers Association. The rock and other materials such as limestone are melted together and the liquid mixture is formed into fibers by machine. Fiberglass is formed by melting glass and sand, then using a machine to spin the glass into fibers. The fibers may be further processed into solid sheets for other products, or woven together for insulation. Both rock wool and fiberglass insulation are fire resistant. Rock wool can resist temperatures topping 2,000 degrees Fahrenheit. Neither type of insulation absorbs water.

Types of Insulation

• Fiberglass and rock wool insulating products are available in loose-fill form and as batting. Batts, or blankets, are thick slabs of insulation that may have a kraft paper facing. The insulation retains its shape for many years and can regain its shape after some compression. Loose-fill fiberglass and rock wool products are, as the names imply, pieces rather than sheets of insulation. This type of insulation suffers less compression and settling than other loose-fill insulation, such as cellulose.

R-Value

• The main difference between rock wool and fiberglass insulation is in the materials' R-values. R-value refers to the insulation's ability to block heat flow, keeping homes cooler in summer and warmer in winter. Rock wool batting provides an R-value of 3.38 per inch of thickness, while an inch of fiberglass batting has an R-value of 3.18. The R-value of blown-in rock wool is 2.75 per inch, and blown-in fiberglass has an R-value of 2.20.

Uses

• Fiberglass and rock wool insulation rolls are generally the same width as the standard space between wall studs or roof joists and may be cut into various lengths according to need. The thickness of the batts determines the insulation's R-value. Loose-fill insulation is used in blown-in insulation applications and is often used to add insulation to existing walls, floors, ceilings and attics. For existing walls, ceilings and floors, a small hole is drilled and a machine forces the insulation into the cavity.

  Besides insulation, rock wool is often used as a soilless growing medium for plants. Fiberglass may be used to make skateboards, boats, shower curtains and other common items.