Blown-in cellulose insulation is a loose-fill product made from recycled wood and paper fibers, and it is one of the most cost-effective ways to insulate an existing home. Installers blow the material into closed wall cavities and attic floors, where it settles into a dense, down-like blanket that conforms around wires, ducts, and pipes. This overview of blown-in insulation compares loose-fill fiberglass and cellulose for attics and wall cavities, so you can see where each product fits before you buy.
Properly installed cellulose keeps houses warmer in winter and cooler in summer, and the energy savings typically recover the installed cost within a few heating seasons. The material is thick, dense, and clumpy, with a consistency often compared to down feathers, and that density is exactly what lets it stop airflow through cavities that batts leave open.
The payoff shows up on utility bills. Insulation upgrades rank among the cheapest home improvements per dollar of energy saved, and blown-in products deliver that return without major demolition. Homes with uninsulated attics lose a large share of their heat through the roof, so filling that one cavity often outperforms window and door upgrades at a fraction of the cost.
What Is Cellulose Insulation?
Commercial cellulose insulation comes from recycled newspapers, cardboard, office paper, and other everyday waste paper, ground into fibers and treated with borates for fire and pest resistance. It belongs to a wider family: the insulation market is built on fiberglass, cellulose, spray foam, and rigid foam, and each behaves differently in walls, attics, and foundations.
Manufacturers report recycled content above 80 percent for most products, and a typical installation lasts 20 to 30 years. The material delivers roughly R-3.2 to R-3.8 per inch, comparable to fiberglass batts, but it packs into irregular cavities and seals around obstructions in a way cut batts cannot match.
Manufacturing is a recycling story. The paper stock is shredded, milled into fibers, and mixed with borate compounds that make up roughly 10 to 15 percent of the finished product by weight. Those same borates give cellulose its fire and pest resistance, so the recycled content is not a marketing claim but the material itself.
How Loose-Fill Differs From Batts
Fiberglass batts arrive in pre-cut rolls that must fit the cavity exactly; loose-fill cellulose is blown in and settles under its own weight, filling every gap. Some settling over time is normal, typically 5 to 10 percent of installed thickness, and installers compensate by overfilling slightly.
Where It Works Best
- Open attic floors, where it can be blown to any depth
- Closed wall cavities in existing homes, using dense-pack
- Retrofits where removing drywall is not an option
- Irregular spaces around pipes, ducts, and wiring
How Blown-In Cellulose Is Installed
Two methods dominate. Dry-blown insulation is used on open attic floors, where a hose delivers loose material to a target depth. Dense-pack installation is used inside wall cavities, where the material is blown under pressure through small access holes. Homeowners researching the product will find practical detail on how cellulose insulation performs once it is in place, including the equipment and labor involved.
The Installation Sequence
- Seal air leaks with caulk and foam before any insulation goes in
- Drill access holes in wall cavities or stage the attic for a loose-fill pass
- Blow the material to the target depth or density for your climate zone
- Patch the access holes and check for voids around obstructions
Attic depth targets follow local codes, with most cold-climate requirements in the R-38 to R-60 range. Dense-pack walls are a job for a professional crew with the right blower; open attic floors are the one part a confident DIYer can handle with rental equipment.
Depth converts to R-value through simple math. At roughly R-3.5 per inch, an attic that needs R-49 takes about 14 inches of settled cellulose, and installers mark the target on attic joists or a depth gauge so the crew can see coverage at a glance. Walls use density rather than depth, with dense-pack targets around 3.5 pounds per cubic foot.
The quote should state a depth, not just a price. Most jurisdictions set minimum R-values that vary by climate zone, and attic insulation depth is one of the most common items checked during energy audits and home inspections. Confirm the target before material is ordered, because blowing to the wrong depth means paying twice for the same cavity.
Wet-Spray Method
New construction often uses wet-spray cellulose, where dampened fibers are sprayed into open wall cavities, then trimmed flush with the studs once dry. The method fills every gap at full density but requires the cavity to dry completely before drywall goes up.
Advantages of Cellulose Insulation
Contractors sometimes call it the hardest-working insulation because it fills gaps other products miss, and the numbers back up the reputation.
Where Cellulose Wins
- High recycled content, typically 80 percent or more
- Strong soundproofing from its dense mass
- Gap-filling performance around wires, ducts, and pipes
- Lower embodied energy than foam products
- Borate treatment provides fire and pest resistance
- Installed cost usually lands between $1 and $3 per square foot
For retrofit work, dense-pack cellulose can be added without opening walls, which makes it cheaper than gutting a room to install batts. The material also stores carbon in the paper fibers for the life of the building.
The acoustic benefit is real and measurable. Dense cellulose absorbs sound far better than fiberglass at the same thickness, which matters for home theaters, bedrooms over garages, and party walls between units. Homeowners who add it for energy often notice the quieter rooms first.
Drawbacks, Moisture, and Placement Mistakes
Cellulose is not without limits. It settles over time, absorbs moisture when exposed to leaks, and must be kept dry to hold its R-value. Getting placement right is half the battle, and understanding proper insulation placement in roofs and walls prevents the problems that come from too much or too little material.
Moisture Rules
- Keep cellulose away from chronic leaks and roof penetrations
- Use a vapor retarder on the warm side in cold climates
- Vent attics properly so humid air escapes
- Install baffles so insulation never blocks soffit vents
Signs of a Bad Install
- Cold spots on walls or ceilings in winter
- Ice dams along the roof edge
- Visible settling below the expected depth
- Damp spots or musty odors in insulated cavities
Retrofit crews watch for a few classic errors. Blowing over recessed light fixtures without insulation-contact-rated housings creates a fire hazard, stuffing material into soffit vents blocks attic airflow, and compressing cellulose to force more into a cavity lowers its R-value because trapped air is what provides the insulation. A quality installer checks each one before declaring the job done.
Cellulose vs. Fiberglass vs. Spray Foam vs. Rigid Foam
Each product trades cost, R-value, and moisture tolerance differently. The table below summarizes typical values for the main options.
| Property | Cellulose | Fiberglass batts | Spray foam | Rigid foam |
|---|---|---|---|---|
| R-value per inch | 3.2 to 3.8 | 3.0 to 3.7 | 6.0 to 7.0 closed cell | 4.0 to 6.5 |
| Recycled content | 80 percent plus | Low | None | Varies by product |
| Air sealing | Good when dense-packed | Poor | Excellent | Good with taped seams |
| Moisture tolerance | Low | Moderate | High | High |
| Installed cost per sq ft | $1 to $3 | $0.50 to $2 | $2.50 to $7 | $1 to $5 |
Where Each Product Fits
Attics take loose-fill cellulose or fiberglass; walls take batts, dense-pack cellulose, or spray foam; basements and foundations take rigid board. For foundation work, slab insulation fundamentals explain the choice between perimeter and full under-slab strategies, a decision that shapes the whole building envelope.
The Cost Question
Cellulose usually wins on price per R-value for attics and retrofits. Spray foam wins on air sealing but costs two to three times more. Rigid board sits in between and earns its place where thin profiles matter, like cathedral ceilings and foundation walls.
Air sealing multiplies any insulation choice. The same blower door test that finds leaks before an install will show the finished result, and houses that seal first see their insulation perform closer to rated values. That pairing matters more than the brand of material on the shelf.
Fire Safety, Eco-Friendliness, and the Decision
Borate-treated cellulose carries a Class A fire rating, and it smolders rather than melting and dripping the way foam can. The treatment also deters insects and rodents, which makes cellulose a common choice in attics where pests are a recurring problem.
Making the Choice
- Budget: cellulose and batts cost the least per square foot
- Retrofit access: dense-pack cellulose works without opening walls
- Moisture risk: foam handles damp spaces better
- Climate: cold zones want more depth and careful vapor control
- DIY scope: attic loose-fill is DIY-friendly; dense-pack is not
Service life is long but not infinite. Most manufacturers warrant cellulose for 20 to 30 years, matching the published lifespan of the material, and performance holds as long as the building stays dry. At end of life, cellulose can be composted or landfilled without the disposal concerns that foam presents, which closes the recycling loop it started with.
For exterior sheathing and foundation walls, rigid foam insulation offers a thin, high-R alternative, and the EPS, XPS, and polyiso boards each have their own trade-offs. Run the numbers for your climate, seal the air leaks first, and match the product to the assembly rather than the other way around.