When it is time to upgrade an underperforming attic in Des Moines to the Department of Energy's recommended R-49 to R-60 (Climate Zone 5), "blown-in" insulation is the undisputed standard. Unlike rolled batts, blown-in material fills every crevice, covering complex framing and completely burying joists. However, the decision between blown-in cellulose and blown-in fiberglass will make a dramatic difference in your home's air quality, draft reduction, and winter heating bills.

What is Blown-In Cellulose?

Cellulose is essentially recycled newsprint and cardboard that has been finely shredded and heavily treated with borate—a compound that is completely harmless to humans but lethal to insects and highly flame-retardant. It is gray, dense, and feels slightly like heavy dust or ground-up fabric.

The Iowa Advantage: Because it is dense, cellulose excels at blocking air movement. In older Iowa homes with leaky top plates, blown-in cellulose naturally settles into gaps and significantly reduces the "wind chill" effect of drafts pulling through the attic floor.

What is Blown-In Fiberglass?

Blown-in fiberglass is manufactured by spinning molten glass into incredibly fine, fluffy fibers (often pink or white). It is extremely lightweight and relies entirely on trapping tiny pockets of air between the glass fibers to slow heat transfer.

The Drawback: While it provides good R-value per inch under perfect laboratory conditions, fiberglass is terrible at stopping air flow. If an attic is not meticulously air-sealed before blow-in, cold January wind will slice right through fiberglass, a phenomenon known as "thermal bypass."

The Settling Factor

A common myth is that cellulose is bad because it "settles." It is true that 15 inches of freshly blown cellulose will settle down to about 12.5 inches over the first year. However, professional contractors know this. They use "stabilized cellulose" and intentionally over-blow the attic by 20% to account for settling, ensuring your final, permanently settled depth achieves a true R-60.

The Verdict for Central Iowa

At an elite contractor level, we highly prefer Cellulose for attic retrofits. Iowa's extreme winter winds are brutal. When you place a highly dense material like cellulose across your attic floor, it actively limits convective heat loss and chokes off drafts much better than a light, fluffy layer of fiberglass.

A properly air-sealed attic capped with 16 inches of borate-treated cellulose is one of the most impenetrable thermal barriers you can put on a Des Moines home.