1. Glass fiber batts will not stop air leakage (it might filter out some dirt and dust). Blown-in cellulose will slow down air leakage. Spray polyurethane insulation will stop air leakage . . . dead.

2. Glass fiber batts have an R-value of about 3.5 (1-inch thickness). Blown-in cellulose has an R-value of about 3 to 4 (1-inch thickness). Spray applied polyurethane insulation has an R-value of 6.5 to 7 (1-inch thickness).

3. Glass fiber batts can sag over time; blown-in cellulose can settle over time: both situations leave sections uninsulated and you’ll feel colder because of it. Spray polyurethane insulation completely adheres to wood and sheathing and is rigid; the result is a permanent barrier to heat loss and air entry.

4. Spray polyurethane insulation will add strength and rigidity to your house. Glass fiber batts and blown-in cellulose will not..