There are three types of blown-in insulation.
The three most common types of blown-in insulation are loose-fill fiberglass, cellulose, and rock wool—each with its own pros and cons.The higher the thermal resistance (R-value), the greater the insulating effect. Not all types of blown-in insulation offer the same thermal value, but in most cases, even adding a little insulation is better than not adding any at all.
- Loose-fill Fiberglass: This light-as-air insulation is manufactured from glass that is heated to a liquid and then spun into thin fibers. When blown into attics and wall spaces, loose-fill fiberglass offers an average R-2.5 thermal value per inch (the higher the number, the greater the insulating effect). You’d need a thickness of about 7.5 inches of insulation to match the insulating value of a batt of R-19 insulation (R-19 is a common batt value). One bag will provide a thermal value of R-19 over a 106.6-square-foot area.
- Cellulose: For eco-minded homeowners, cellulose is often the insulation of choice, because it’s made from finely shredded recycled cardboard or newspaper. This is the most common type of blown-in insulation on the market, and it’s chemically treated to resist mold and fire. A downside to cellulose is that if it gets wet (from a leaky roof or pipe), it can lose its fluffiness and become soggy and compacted, which reduces its R-value. Cellulose insulation has an average thermal value of R-3.7, so you’d need just over five inches to equal an R-19 batt. A bag of cellulose runs and will cover 36.7 square feet at a thermal value of R-19.
- Rock Wool: Also called “mineral wool,” this type of blown-in insulation is made from blast furnace slag (a byproduct of firing iron and iron ore). The slag is heated, combined with other minerals, and then spun into an airy product that resembles the texture of raw sheep’s wool. Rock wool features a thermal value of R-3.3 per inch, but it is much more expensive than either loose-fill fiberglass or cellulose—a single bag will only cover 60 square feet at a thermal value equal to R-19. Despite its high price point, due to its excellent fire resistance, rock wool is often called for in areas subject to fire codes, such as a connecting wall between a house and an attached garage, or in the floor between a garage and a FROG room (finished room over garage)