Insulation Options

There are all kinds of materials to stuff in, nail on, spray on, or blow into walls and ceilings to lower your heating and cooling bills. Weigh your choices based on all the factors, including the abilities of the installer and the long-term energy savings.


A. Cotton Batts
No-itch batts of recycled denim from jeans factories are treated with borates to resist fire and insects. Good for: New construction, attics
R-value per inch: 3.7
Vapor barrier needed: Yes
Cost: 70¢ to 75¢ per sq. ft.

B. Loose-Fill Fiberglass
Fluffy bits of spun glass that are noncombustible and can't decay. Blown in dry. Tends to settle. R-value declines by as much as 50 percent at temps below 0 degrees F.
Good for: Attic insulation, new construction, or retrofit work
R-value per inch: 4
Vapor barrier needed: Yes
Cost*: 21¢ per sq. ft.

C. Extruded Polystyrene (XPS)
Its closed-cell structure stops water and water vapor, resists compression, and holds its R-value over time. Must be protected from solvents and sunlight. Flammable and must be protected from fire with drywall or plaster.
Good for: In-ground foundation insulation, masonry structures
R-value per inch: 5
Vapor barrier needed: No
Cost: 50¢ per sq. ft. for a 2-in.-thick panel

D. Cellulose
Made from pulverized newspapers and treated with boron to resist fire and pests. Blown into place dry or wet. An adhesive reduces its tendency to settle. Good for: Retrofit work, attic insulation
R-value per inch: 3.8
Vapor barrier needed: No, if packed to a density of at least 2.6 lb./cu. ft.
Cost: 17¢ per sq. ft.

E. Fiberglass Batts
Lightweight batts of spun glass offer a predictable R-value if not compressed, but the fibers offer little resistance to air movement and convective heat loss. The sample shown is held together with a nontoxic acrylic binder instead of the typical formaldehyde-based binder.
Good for: New construction, attics
R-value per inch: 3-4
Vapor barrier needed: Yes
Cost: 38¢ per sq. ft.

F. High-Density Polyurethane Spray Foam
The rigid, closed-cell structure makes it impermeable to water. Must be professionally applied. While not flammable, it must be protected with drywall or plaster to stop offgassing during a fire.
Good for: Masonry basement walls
R-value per inch: 7
Vapor barrier needed: No
Cost: 4 times the cost of fiberglass batts

G.Mineral Wool
Spun from blast-furnace slag, this inorganic insulation does not burn or support the growth of mold or mildew. Highly sound-absorbent. Blown into place wet, it's trimmed flush with the studs after it dries; the trimmings are recycled.
Good for: New construction, attics
R-value per inch: 4
Vapor barrier needed: Yes
Cost: 19¢ per sq. ft.

H. Low-Density Polyurethane Spray Foam
Blocks the movement of air (eliminating the need for a vapor barrier), absorbs sound like a sponge, and flexes with the seasonal movement of the framing. Must be professionally applied. Although not flammable, must be protected from fire with drywall or plaster.
Good for: New construction, or retrofit in attics or crawl spaces
R-value per inch: 4
Vapor barrier needed: No
Cost: 4 times the cost of fiberglass batts.

I. Foil-Faced Polyisocyanurate
Its closed-cell structure stops water vapor, and the foil-covered face acts as a radiant barrier. Not recommended for exterior, below-grade applications. Not flammable, but it must be protected with wallboard.
Good for: Cathedral ceilings, walls for finished basements
R-value per inch: 7-8
Vapor barrier needed: No
Cost: 40¢ per sq. ft. for a 3/4-in.-thick panel

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