Loose-fill insulation is usually made of cellulose (recycled paper) or fiberglass, although mineral wool and cotton loose-fill are also available. A very general estimate of its cost per square foot per R-value (see our What to Look For page for an explanation of R-value) is $0.015 to $0.02 for cellulose and $0.01 to $0.015 for fiberglass, not installed. Loose-fill is typically used in wall cavities and attics. It is well suited for hard-to-reach areas, such as behind plumbing or in tight corners. Loose-fill insulation is particularly useful for adding insulation in existing homes because, except for the small holes that are drilled for installation in closed wall cavities, it is one of the few types of insulation that can be installed without greatly disturbing existing finishes. It can also be blown in on top of existing insulation in attics.
Loose-fill insulation is usually professionally installed, but you can rent the equipment from building-supply retailers and do it yourself (though some manufacturers recommend against this). Since both fiberglass and cellulose loose-fill insulation tend to settle, losing thickness and thus R-value, either type should be installed to the "settled" R-value (rather than the initial R-value) provided by the manufacturer. Cellulose loose-fill is sometimes mixed with water and an adhesive and blown in damp to prevent settling.
Cellulose and fiberglass loose-fill insulation have similar R-values (generally between 3 and 4 per inch), but beyond that they differ, with each having some advantages and disadvantages. Most green building experts consider cellulose the greener material since it's made from recycled paper and takes less energy to manufacture than fiberglass does. (Fiberglass insulation often contains up to 40 percent recycled content as well.) Cellulose is also denser than fiberglass, which makes it less air permeable; unlike fiberglass, it does not lose R-value when outside temperatures are very low.
The increased density of cellulose insulation may be a concern when it's installed in an attic. To get an equivalent total R-value with cellulose requires putting more weight on the ceiling drywall than with fiberglass, and too much weight could cause a ceiling to sag, depending on its construction. If a high R-value is required in your climate zone and you want to use cellulose, be sure to check your ceilings' weight limits. Some cellulose manufacturers put weight limit information on the packaging.
Need help figuring out how much insulation and what R-value you need? See our What to Look For page for details on those calculations, plus installation considerations and other factors to consider.