For a simple, open attic floor with easy access, blown-in cellulose is a cost-effective way to add a lot of R-value, as long as the air leaks underneath are sealed first. Spray foam is the stronger choice when you need air sealing built in, when the attic has ductwork or a furnace you want inside the insulated space, or when the space is a cathedral ceiling, knee wall, or bonus room where loose fill won't stay put. Many Iowa attics end up using both: foam to seal, cellulose t