Types of Insulation:
R-Values, Costs &
Where Each One Works

There are really only a handful of types of insulation, and every product on the shelf falls into one of them: blankets (batts and rolls), loose-fill that gets blown in, rigid foam board, spray foam, and a few specialty systems like radiant barriers, SIPs and insulated concrete forms. We manufacture spray foam, so we have a horse in this race, but we also work on plenty of houses where the right answer is a truckload of blown cellulose or a stack of foam board. This guide lays out each type of insulation honestly: what it is made of, its R-value per inch, what it costs installed in 2026, where it works and where it fails.

Insulation types compared: R-value, cost and air sealing

R-values per inch come from DOE, ASTM C578 and manufacturer data sheets; installed costs are 2026 national ranges from HomeGuide and Angi. Treat costs as a sanity check, not a quote. Click any heading to sort.

How to read the cost column

Per-square-foot prices hide the depth. HomeGuide puts blown-in R-30 at $660 to $1,200 per 1,000 sq ft of attic floor, so roughly a dollar a square foot buys R-30. Closed-cell foam material alone runs $0.90 to $1.00 per board foot, and a board foot is one inch over one square foot, roughly R-6.5, before any labor. That is why we tell people not to use spray foam where a cheaper type can do the job. Our spray foam insulation cost guide breaks down the board-foot math in detail.

Why R-value alone misleads you

R-value is measured on a clean lab sample at a 75°F mean temperature with no air moving through it. Your attic in January is not that lab.

1. Air leakage goes straight through most insulation

Fiberglass, mineral wool and loose-fill are filters, not air barriers. EPA's 15% savings estimate assumes air sealing (a 25% cut in infiltration) as well as insulation. Spray foam is the exception: it is the insulation and the air seal in one layer, and dense-packed cellulose slows air substantially.

2. Temperature changes the number

Building Science Corporation testing reported by Green Building Advisor found polyiso that delivers about R-6 per inch in summer can fall to roughly R-4.5 on a cold winter day; roofers design cold-climate roofs at R-5 per inch. XPS goes the other way: Owens Corning lists FOAMULAR 250 at R-5.0 per inch at 75°F and R-5.4 at 40°F. Oak Ridge National Laboratory reported in 1991 that convection cut loose-fill fiberglass effectiveness by 30% when attic temperatures fell below about 0°F.

3. Some types lose R-value or depth over time

Cellulose settles up to 20%, so bag charts list a smaller settled thickness. Foams made with gas blowing agents age as gas diffuses out, which is why polyiso is rated by long-term thermal resistance (LTTR), a 15-year time-weighted average; the design value for permeable-faced polyiso roof board was cut from R-6.0 to R-5.7 per inch in 2014.

4. Moisture and vapor behavior

Fibrous insulation is vapor-open: it lets a wall dry, but vapor control has to come from somewhere else. Foam boards range widely: DOE lists foil-faced polyiso at about 0.03 perms, 1 inch of XPS at 1.1 perms and 2 inches at 0.55, and EPS from 2 to 5 perms depending on density. Closed-cell spray foam becomes a vapor retarder at typical wall depths; open-cell does not.

5. Fire behavior

Mineral wool is noncombustible (ASTM E136) with a melting point near 2,150°F. Cellulose is treated with fire retardants and must pass the federal CPSC standard (16 CFR 1209) for radiant flux and smoldering. Every foam plastic, board or spray, has to be separated from living space by a code-approved thermal barrier such as 1/2 inch gypsum board. That includes our foam; see spray foam insulation problems.

Best type of insulation for each part of the house

1. Attic floor

   Loose-fill cellulose or fiberglass, blown to R-49 or R-60 in most climates after the ceiling plane is air sealed. Our attic insulation cost guide covers when foaming the roof deck makes more sense instead.

2. Cathedral ceilings and roof decks

   Shallow rafter bays need high R per inch and an air seal. Closed-cell foam, or foam board above the deck, is usually the answer. See cathedral ceiling insulation.

3. Existing closed walls

   Dense-pack cellulose blown through small holes is the standard retrofit. Injection foam is the other option for masonry and some frame walls; our injection foam guide covers it.

4. Open stud walls

   Batts (fiberglass or mineral wool) are the budget route; open-cell or closed-cell foam costs more but seals every wire and box penetration.

5. Basements and crawl spaces

   Insulate the foundation walls with materials that tolerate moisture: XPS, EPS or closed-cell foam against the concrete. DOE says an insulated basement can cut heating bills 10% to 20%. See basement wall insulation and crawl space insulation.

6. Rim joists

   Closed-cell foam or cut-and-sealed foam board; fiberglass stuffed in the bay does little for air leaks. Details in our rim joist insulation guide.

7. Metal buildings and pole barns

   Closed-cell foam applied directly to the panels insulates and stops condensation on the steel; faced fiberglass blankets are the low-cost alternative. Compare both in metal building insulation.

Where we would not use spray foam

We sell closed-cell and open-cell spray foam, and we still tell people to skip it on an open, accessible attic floor (loose-fill is cheaper per R), in a wall that is already closed (dense-pack or injection foam is less disruptive), and on any job where the budget only allows a thin coat to "seal things up." Spray foam earns its cost where air sealing, moisture control and R per inch all matter at once.

Types of insulation: common questions