For homeowners

Types of attic insulation: which one fits your attic?

Choose Fiberglass batts or rolls for a do-it-yourself job; Blown-in loose fill (cellulose or fiberglass) for attics with wires, ducts and pipes; Spray foam (closed-cell or open-cell) for an unvented attic in a cold or humid climate.

The right choice depends on whether your attic is vented or unvented, your climate, whether wires, ducts and pipes run across the attic floor, and whether you plan to do the work yourself.

How we know: By InstaBids editorial team with AI research agents. · Sources read: 17 October 2026 · Updated 27 October 2026

Spray foam here means foam-in-place insulation, which DOE says comes as closed-cell or open-cell and is typically made with polyurethane.
Type	Best for	Main advantages	Main drawbacks
Fiberglass batts or rolls	a do-it-yourself job	DOE/PNNL (2012): a good choice for insulating the floor of a vented attic; DOE (2022): comes in widths suited to the standard spacing of attic or floor joists	DOE/PNNL (2012): not air-tight; air leaks around the edges significantly reduce R-value, so careful installation is necessary
Blown-in loose fill (cellulose or fiberglass)	attics with wires, ducts and pipes	DOE/PNNL (2012): the small particles conform to the space they are blown into; well suited for retrofits; DOE/PNNL (2012), blown fiberglass: non-flammable; DOE/PNNL (2012): loose-fill fiber is a good choice for insulating the floor of a vented attic	DOE/PNNL (2012), cellulose: requires chemical treatment with fire retardant and must be kept away from chimneys and metal flues; DOE/PNNL (2012), cellulose: wetting and high humidity can make it absorb large quantities of water, reducing thermal resistance; DOE/PNNL (2012), blown fiberglass: many blowing machines over-fluff it in attics, reducing density and R-value; it goes in with a blowing machine, so ENERGY STAR says it may be wise to hire a professional
Spray foam (closed-cell or open-cell)	an unvented attic in a cold or humid climate	DOE/PNNL (2012), closed-cell foam: very resistant to moisture and an excellent air barrier; DOE (2022): can be blown onto attic surfaces to insulate and reduce air leakage	DOE (2022): consider hiring a professional to install foam insulation; DOE/PNNL (2012), open-cell foam: not a vapor retarder

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What type of insulation is best for an attic?

It depends on whether the attic is vented. For the floor of a vented attic, DOE's Building America insulation guide (2012) says "loose-fill fiber and fiberglass batts, are good choices for insulating the floor of a vented attic".

For an unvented attic, the same guide (2012) says: "In cold or humid climates, unvented attics should be insulated with rigid or spray foam insulation". It adds: "In the hot-dry climate zone, you can insulate an unvented attic along the underside of the roof deck" with fiber insulation, and "However, in all other climates, insulating the underside of the roof deck with fiber insulation could lead to moisture problems".

Is 4 inches of attic insulation enough?

ENERGY STAR recommends adding more: for an attic that already has 3–4 inches of insulation, its table recommends adding R25 in climate zone 1, R38 in zones 2 and 3, and R49 in zones 4 through 8.

For an uninsulated attic the same table recommends R30 in zone 1, R49 in zones 2 and 3, and R60 in zones 4 through 8. The table covers retrofitting existing wood-framed buildings, and ENERGY STAR says the guidance is based on the 2021 International Energy Conservation Code (IECC).

What is the downside of cellulose insulation?

DOE's Building America insulation guide (2012) lists these among the disadvantages of blown-in cellulose: "Requires chemical treatment with fire retardant. Cellulose must be kept away from chimneys and metal flues."

The same guide (2012) says: "Accidental wetting and high humidity can cause cellulose to absorb large quantities of water, reducing thermal resistance". Of blown-in loose fill in general, it says it "Can have settlement problems if not installed properly."

What are the different types of roof insulation?

DOE lists batts, blown-in fiberglass or cellulose, spray foam, rigid foam and SIPs: "Ceilings and roofs can be insulated using batts, blown-in fiberglass or cellulose, spray foam, rigid foam, or SIPs."

For an unvented attic outside the hot-dry climate zone, one of the ways the same DOE guide (2012) gives to prevent condensation under the roof deck is: "Use spray foam insulation under the roof deck to keep interior moist air from contacting it."

If your priority is...
Priority	Choose
laying the insulation in yourself	Fiberglass batts or rolls
wires, ducts and pipes running across the attic floor	Blown-in loose fill (cellulose or fiberglass)
an unvented attic in a cold or humid climate	Spray foam (closed-cell or open-cell)

What does attic insulation cost?

For prices, see How much does attic insulation cost?

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Sources for the facts on this page

ENERGY STAR (U.S. EPA), Attic Insulation Project, government, read 17 October 2026.
U.S. Department of Energy, Energy Saver Guide (2022), government, read 17 October 2026.
U.S. DOE Building America Best Practices Series Vol. 17, Energy Renovations: Insulation (PNNL-20972, prepared by Pacific Northwest and Oak Ridge National Laboratories, May 2012), government, read 17 October 2026.
ENERGY STAR (U.S. EPA), Recommended Home Insulation R-Values, government, read 17 October 2026.
U.S. Department of Energy, Building Science Education Solution Center, Types of Insulation, government, read 17 October 2026.