Cellulose can be found in attics, walls, ceilings and other places around the home. It's mostly made of shredded newspaper, which makes it quite combustible. Although cellulose insulation is generously treated with fire retardant, it isn't fireproof. Cellulose installation also absorbs and retains moisture. If soaked, its thermal performance can be permanently diminished. Cellulose insulation can be applied a variety of ways. One method is to add water to it; however, this wet-spray method does not achieve full R-value until dry.
Insulation made of cellulose uses the same amount of virgin materials as that used to make fiberglass. However, it takes up to three times more cellulose than fiberglass to achieve the same insulating efficiency. Cellulose not only settles much more than other types of insulation (20 percent), but it does so at a higher rate. This is why the Insulation Contractors Association of America recommends adding 25 percent thickness to cellulose insulation to compensate for major R-value loss.