For homeowners

Closed cell vs open cell spray foam insulation: which fits your home?

On DOE and Building America Solution Center guides: choose Closed-cell spray foam for vapor retarding (slowing water vapor moving through walls and other building materials) in cold climates that require more protection from condensation (DOE, 2012); Open-cell spray foam for an unvented attic's roof cavity filled with foam in International Energy Conservation Code (IECC) Climate Zones 1 through 3, where interior humidity is not high (DOE, 2012, on 2006 research).

The right choice depends on how cold your climate is (your climate zone on the International Energy Conservation Code map), whether the air inside your home is humid, and where the foam goes: filling the roof cavity under the deck or sealing an existing attic floor.

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

DOE (2012), for both foams: "Plastic foam insulation must be covered with a thermal barrier to retard the spread of fire."
Factor	Closed-cell spray foam	Open-cell spray foam
Vapor retarding (slowing water vapor moving through walls and other building materials) in cold climates that require more protection from condensation (DOE, 2012)	also a vapor retarder, an advantage in cold climates that require more protection from condensation	not a vapor retarder
An unvented attic's roof cavity filled with foam in International Energy Conservation Code (IECC) Climate Zones 1 through 3, where interior humidity is not high (DOE, 2012, on 2006 research)	the same 2006 research list: "In Zones 6 and higher, closed-cell foam should be used."	can be used there, provided interior humidity is not high (2006 research)
A vapor control layer under the roof deck, the layer that limits moisture moving through the roof (DOE Building America Solution Center)	can serve as both the thermal control layer and the vapor control layer	vapor open: it cannot act as a vapor control layer
An air-sealing layer on an existing attic floor (DOE Building America Solution Center)	the product the guide names as preferred for this air barrier application	its expansion can leave billows and voids that make a continuous, uninterrupted layer difficult
Drawbacks DOE's insulation table lists, besides cost	"Installation difficult. Requires a fire barrier."	"Installation difficult."

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If your priority is...
Priority	Choose
vapor retarding in a cold climate that requires more protection from condensation (DOE, 2012)	Closed-cell spray foam
an air-sealing layer on an existing attic floor (DOE Building America Solution Center)	Closed-cell spray foam
foam filling an unvented attic's roof cavity in IECC Climate Zones 1 through 3, where interior humidity is not high (DOE, 2012, on 2006 research)	Open-cell spray foam

What does attic insulation cost?

For attic insulation prices, see How much does attic insulation cost?

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Sources for the facts on this page

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.
U.S. DOE Building America Solution Center (Pacific Northwest National Laboratory), Unvented Conditioned Attic - Spray Foam Insulation below Roof Deck (last updated 2020-09-11), national laboratory, read 17 October 2026.
U.S. DOE Building America Solution Center (Pacific Northwest National Laboratory), Spray Foam Insulation Applied to Existing Attic Floor (last updated 2022-11-27), national laboratory, read 17 October 2026.