Cellulose insulation is a type of wood- or paper-based product. It is used to fill empty spaces in the structural part of a house to slow down the transmission of heat or cold. Cellulose insulation is thick, dense, and clumpy, with a consistency much like down feathers. The chief value of this shape and size is that the insulation can fit in enclosed areas (such as walls) and can conform around obstructions such as wires and ducts (found both in walls and in attics).
Commercial cellulose insulations are generally derived from wood, and more specifically from paper: recycled newspapers, cardboard, office paper, and other common waste paper products. For this reason, cellulose insulation is considered an eco-friendly home product.
Cellulose Insulation Advantages
There are a number of advantages to using cellulose insulation over other types:
Loose-fill cellulose insulation can settle around and conform to most of the obstructions found in walls and attics.
Loose-fill cellulose is relatively inexpensive, yet still has an R-value of about 3.5 per inch of thickness, compared to fiberglass' R-value between R3 to R4 per inch.
When walls are already finished, injecting loose-fill cellulose insulation is one of the few ways of adding insulation. One alternative is to pull down the drywall and use fiberglass batts.
Cellulose insulation stands up reasonably well against insects and vermin because it is treated with borates.
Cellulose Insulation Drawbacks
There are also a few drawbacks to cellulose insulation:
While settling is one of blown-in cellulose insulation's advantages, this can also be a problem, mostly with walls. Over time, the insulation can pack down and form pockets above the settled areas. These pockets become thermal bridges, which transmit heat or cold into the house. Settling in attics is less problematic for two reasons. First, attic spaces can be overfilled to account for settling. Second, when cellulose insulation in attics settles, no empty spaces are formed.
When cellulose soaks up moisture in enclosed areas, it can take a long time to dry out. Moisture dramatically cuts R-value and may lead to the formation of mold and mildew. Rigid or sprayed-in foam stands up better against moisture.