Why Cellulose Insulation Excels in Attics! Why is cellulose the smarter choice for attic insulation? At Advanced Thermal Concepts, we recommend Greenfiber cellulose insulation because it outperforms fiberglass in nearly every category. Here’s why: ☀️ Stops radiant heat – fiberglass doesn’t block radiant transfer, but cellulose slows it down, keeping your home cooler in summer. ❄️ Winter protection – cellulose limits air infiltration far better than fiberglass, holding warm air in when the attic