Cellulose Insulation:
R-Value, Cost, Pros & Cons
for Attics and Walls

Cellulose insulation is shredded recycled paper treated with fire retardants and blown into attics and walls. It is one of the best values in residential insulation: about R-3.6 per inch on an attic floor, cheap per R-value, and dense enough when packed into a wall to slow air leakage in a way fiberglass cannot. We manufacture spray foam, and we still recommend cellulose for most open attic floors and for retrofitting closed walls in older houses. This guide covers how cellulose insulation is made and installed, how it compares, what it costs, its real drawbacks, and two calculators: one for attic bags and depth, one for dense-packing walls.

Cellulose vs fiberglass vs spray foam

Cellulose competes mainly with blown fiberglass in attics and with batts or injection foam in walls. The numbers below are 2026 installed ranges and published R-values; sort by any column.

Where cellulose beats fiberglass

Per inch, cellulose has a higher R-value than blown fiberglass, so you need less depth for the same R: on the manufacturers' own charts R-49 is about 15 inches of GreenFiber cellulose versus 17 inches of Owens Corning AttiCat. It is denser, which matters in cold attics: Oak Ridge National Laboratory reported in 1991 that convection through air-permeable loose-fill fiberglass cut its effectiveness by 30% when attic temperatures dropped below about 0°F. And dense-packed in a wall it slows air movement through the cavity.

Where fiberglass beats cellulose

Fiberglass is much lighter. At R-60, GreenFiber's chart calls for 2.26 pounds of cellulose per square foot of ceiling versus 0.87 pounds of AttiCat. On older or questionable ceilings, that weight is worth a look before you blow R-60 of cellulose on top. Fiberglass also does not absorb water, so a roof leak is less likely to leave a soggy, compressed patch.

Dense-pack cellulose wall calculator

Dense-packing is how most old, empty walls get insulated without tearing off siding or plaster: the installer drills a hole in each stud bay, inserts a tube and blows cellulose until the bay is packed hard. Use this to size the job and sanity-check a quote.

Before dense-packing an old house, look for knob-and-tube wiring (it should be evaluated by an electrician before it is buried in insulation), check that the exterior keeps water out, and make sure bays under windows and above headers get filled; those are the ones missed most often. Ask the installer how they verify fill, such as by tracking bag weight per bay or with an infrared scan on a cold day.

How a good attic cellulose install goes

1. Air seal the attic floor

   Foam or caulk every top plate, wiring and plumbing hole, flue chase (with fire-rated material), and recessed light. This is the step that separates a good insulation job from a pile of paper.

2. Baffles, dams and clearances

   Install vent baffles at the eaves so insulation does not block soffit air, build a dam around the hatch, and keep required clearances around chimneys and non-IC-rated fixtures.

3. Depth markers

   Staple depth rulers to trusses across the attic so you and the installer can see the installed thickness.

4. Blow to the chart

   Blow evenly to the initial thickness on the bag chart for your target R-value, using at least the listed number of bags for the area.

5. Get the paperwork

   The FTC's R-Value Rule (16 CFR Part 460) requires loose-fill installers to give you a signed, dated receipt showing coverage area, initial installed thickness, minimum settled thickness, R-value and the number of bags used. Keep it with your house records.

When spray foam is the better call

Cellulose on the attic floor assumes the attic stays vented and outside the house. When the furnace and ductwork live up there, or the roof is a cathedral ceiling with no attic at all, insulating the roof deck with spray foam keeps that equipment inside the conditioned space; see attic foam insulation and our attic insulation cost guide, which compares both approaches. Rim joists, crawl space walls and basements are also foam or board territory, not cellulose. And for closed masonry walls or homeowners who want to avoid drilling every bay from outside, injection foam is the alternative to dense-pack.

Compare other insulation types