What is the best blown-in insulation for an attic?

The best blown-in insulation for an attic depends on your priorities, but for most homeowners, blown-in fiberglass and blown-in cellulose are both excellent, with slightly different strengths. For best overall performance with low dust and good coverage, Johns Manville Climate Pro formaldehyde-free blown-in fiberglass is considered top-tier by contractors. It is lightweight, so it adds less weight to ceiling drywall than cellulose, it does not settle as much over time, and it is treated to resist mold. Owens Corning AttiCat expanding blown-in fiberglass and PINK Fiberglas blown-in are also very good and widely available at Home Depot with free blower rental. For best value and eco-friendliness, GreenFiber and Applegate cellulose blown-in insulation are excellent choices. Cellulose is made from 85 percent recycled newspaper treated with borate for fire and pest resistance, costs about 20 percent less per R-value than fiberglass, and provides slightly better air sealing and soundproofing because it is denser. It has an R-value of about R3.5 to R3.7 per inch versus R2.5 for blown fiberglass. The downsides of cellulose are that it is heavier, dustier during installation, and can absorb moisture if a roof leaks. For attics that already have some insulation, either type can be blown over existing insulation to reach R38 to R60. Most energy auditors recommend cellulose for best bang for the buck and fiberglass for homes with weight concerns or older drywall.