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What are the main types of blown-in attic insulation?

Three materials get blown into attics: fiberglass, cellulose, and mineral wool. Compare R-value per inch, settling, and where each fits.

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What are the main types of blown-in attic insulation?

What gets blown into an attic?

Three materials get blown in: fiberglass, cellulose, and mineral (rock or slag) wool. All are installed with pneumatic equipment, usually by a professional, and work well on unfinished attic floors and around obstructions, per the Department of Energy. Fiberglass and cellulose are the most common in US attics; mineral wool is less widely used.

  • Fiberglass loose-fillR-2.2-R-2.7 per inch; light, settles very little
  • CelluloseR-3.2-R-3.8 per inch; recycled-content, fire-treated, settles ~13%
  • Mineral woolStrong fire and moisture resistance; similar per-inch range to cellulose, less common
  • InstallationAll three are blown in with pneumatic equipment, usually by a professional
  • Where it's usedUnfinished attic floors and areas with obstructions - wiring, joists, pipes
  • Topping upAll three can be blown over existing insulation to raise an under-insulated attic
What gets blown into an attic?

Sources

2 cited
  1. Blown-in material types and where each is used: U.S. Department of Energy, Insulation Fact Sheet, DOE/CE-0180, 2008 (checked 2026-08-19).
  2. R-value per inch for fiberglass and cellulose: U.S. Department of Energy, Building America Solution Center, Loose-Fill Insulation (checked 2026-08-19).
How it works

How blown-in insulation is actually installed

Four steps, done in order. The Department of Energy is explicit that skipping the air-sealing step is the most common way a new insulation job still leaves an attic underperforming.

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  1. 1

    Air seal first

    The EPA recommends sealing attic-floor penetrations before insulating, because loose-fill does not stop air moving through gaps around wiring, pipes and fixtures.

  2. 2

    Add baffles and depth markers

    Rafter baffles keep blown material off the eaves where it could get wet, and depth rulers mark the target R-value before the blower starts.

  3. 3

    Blow to depth

    A pneumatic machine feeds loose fiberglass or cellulose over the attic floor, covering the tops of the joists so heat cannot bypass the insulation.

  4. 4

    Verify and clean up

    The settled depth gets checked against the target R-value for your climate zone, then tools and debris are cleared.

How we work

What this site will and will not do

We explain the R-value target and the real cost drivers first, and we do not sell you the installation - which is why we can say plainly when topping up beats a full replacement.

01

R-value before a quote

ENERGY STAR recommends R-30 to R-60 depending on your climate zone. Knowing your target before you call means you can hold every bid to the same number.

02

Air sealing first, always

The Department of Energy is explicit that insulation slows heat flow but does not stop air leaks - sealing gaps first is what makes the insulation you pay for actually perform.

03

We are not the installer

We do not install anything ourselves, so we have nothing to gain from steering you toward the bigger job. Licensed local companies do the work and quote it themselves.

04

Nothing we cannot source

Every figure on this site traces to a named, dated source - HomeAdvisor, the DOE, ENERGY STAR, the EPA or the FTC. Where we have not sourced a number, we say so instead of guessing.

Questions

Frequently asked

The questions people actually type before calling a company.

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What are the three main types of blown-in attic insulation?

Fiberglass, cellulose, and mineral (rock or slag) wool. Fiberglass and cellulose are the most common in US attics; mineral wool is less widely used but offers strong fire and moisture resistance.

Can all types of blown-in insulation go over existing insulation?

Yes - fiberglass, cellulose, and mineral wool can all be blown over sound existing insulation to top up an under-insulated attic.

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