What is the best type of insulation?

The best insulation depends on the application. For attic floors: blown fiberglass or cellulose is the most cost-effective. For walls in new construction: fiberglass batts or mineral wool batts offer good value. For maximum energy efficiency: closed-cell spray foam provides the highest R-value per inch (R-6-7) plus air sealing, but costs 3-5x more. For sound insulation: mineral wool is best. For retrofitting existing walls without opening them: dense-pack cellulose. For basements: rigid foam board or closed-cell spray foam (moisture resistance is critical). There is no single best insulation — match the type to the specific location and your budget. How much does insulation cost?

How much does insulation cost?

Fiberglass batts: $0.30-$0.50/sq ft (most affordable DIY option). Blown fiberglass or cellulose in attic: $0.50-$1.00/sq ft (professionally installed). Mineral wool batts: $0.60-$1.20/sq ft. Open-cell spray foam (3.5 inches): $1.75-$3.50/sq ft. Closed-cell spray foam (3.5 inches): $3.50-$7.00/sq ft (most expensive). For an average 1,000 sq ft attic: blown insulation costs $500-$1,000 professionally installed. For an average home's exterior walls (1,500 sq ft): fiberglass batts cost $450-$750 in materials. Spray foam would be $2,600-$10,500 for the same walls. What R-value do I need?

What R-value do I need?

R-value requirements depend on your climate zone (IRC 2021 minimums): Climate Zones 1-2 (South Florida, Gulf Coast): R-13 walls, R-30 attic. Zone 3 (Southeast, Southwest): R-20 walls, R-30 attic. Zone 4 (Mid-Atlantic, lower Midwest): R-20 walls, R-49 attic. Zones 5-8 (Upper Midwest, Northeast, Mountain): R-20+5ci walls (ci = continuous insulation), R-49 attic. These are minimums — exceeding code requirements saves more energy. Adding insulation to an existing home is one of the best energy upgrades: attic insulation typically pays for itself in 2-5 years through lower heating and cooling bills. Spray foam vs fiberglass — which is better?

Spray foam vs fiberglass — which is better?

Spray foam is technically superior (higher R-value, air sealing, moisture barrier) but costs 5-10x more. Fiberglass batts at $0.30-$0.50/sq ft vs closed-cell spray foam at $3.50-$7.00/sq ft for the same wall. For most budget-conscious homeowners, fiberglass batts combined with proper air sealing (caulk and foam around penetrations) provides 80-90% of spray foam's performance at 10-20% of the cost. Spray foam is worth the premium for: rim joists (small area, big impact), cathedral ceilings (no other good option), and extremely tight energy targets. For standard attics and walls, fiberglass or cellulose with air sealing is the best value.

Article

Comparisons

Insulation Types Compared: R-Value, Cost, Where to Use & Best Choice

Lumberama Editorial Team, Insulation & Energy Efficiency Specialists Apr 20, 2026 9 min read

Fiberglass

Types: Batts and rolls (pre-cut): fits between studs and joists. Blown-in (loose fill): machine-blown into attics and closed cavities.

R-value: Batts: R-3.1 to R-3.4 per inch. Blown: R-2.2 to R-2.7 per inch.

Cost: Batts: $0.30-$0.50 per square foot (DIY). Blown attic: $0.50-$1.00/sq ft (professional).

Best for: Attics (batts between joists or blown over joists). Wall cavities (batts during new construction). Floors over crawl spaces.

Pros: Most affordable. DIY-friendly (batts). Non-combustible. Does not absorb moisture.

Cons: Does not air seal (air passes through it). Loses R-value when compressed or wet. Irritating fibers (wear protection). Can sag in walls over time. Rodents and insects can nest in it.

Spray Foam

Types: Open-cell: R-3.5-3.7 per inch. Soft and flexible. Lower cost. Absorbs water (not for exterior below-grade). Good sound dampening. Closed-cell: R-6.0-7.0 per inch. Rigid and dense. Also acts as vapor barrier. Structural strength (adds wall rigidity). Higher cost.

Cost: Open-cell: $0.50-$1.00/sq ft per inch. Closed-cell: $1.00-$2.00/sq ft per inch. Full wall (3.5 inches): Open-cell: $1.75-$3.50/sq ft. Closed-cell: $3.50-$7.00/sq ft.

Best for: Rim joists and band joists (air sealing). Cathedral ceilings (no ventilation needed with closed-cell). Crawl spaces (closed-cell on walls). Existing walls (injection foam for retrofit). Irregular spaces and gaps.

Pros: Best air sealing (fills every gap). Highest R-value per inch (closed-cell). Moisture barrier (closed-cell). Does not sag or settle.

Cons: Most expensive. Professional installation required. Cannot be easily removed or modified. Off-gassing during installation (must vacate). Some types use HFC blowing agents (environmental concern).

Cellulose

Types: Blown-in (loose fill): machine-blown into attics and existing wall cavities. Dense-pack: blown at higher density into walls (retrofit). Wet-spray: sprayed with water adhesive into open walls (new construction).

R-value: R-3.2 to R-3.8 per inch.

Cost: Blown attic: $0.50-$1.00/sq ft (professional). Dense-pack walls: $1.00-$2.00/sq ft.

Best for: Attic floors (blown over existing insulation). Retrofit wall insulation (dense-pack through small holes). Older homes with no existing insulation.

Pros: Made from recycled paper (eco-friendly). Good air sealing when dense-packed. Fire-retardant treated (borate). Fills irregular cavities well. Cost-effective for attic upgrades.

Cons: Absorbs and retains moisture. Settles over time in attics (10-20% settling). Heavier than fiberglass (check ceiling load). Dusty installation. Can attract pests if borate treatment degrades.

Mineral Wool (Rockwool)

Types: Batts: pre-cut like fiberglass, but denser and more rigid. Boards: rigid panels for exterior sheathing.

R-value: R-3.3 to R-4.2 per inch (higher than fiberglass).

Cost: Batts: $0.60-$1.20/sq ft. Boards: $1.00-$2.50/sq ft.

Best for: Sound insulation (interior walls between rooms). Fire-rated assemblies (non-combustible, melts at 2,150°F). Exterior continuous insulation (rigid board). Basement walls.

Pros: Fire-resistant (much better than fiberglass). Excellent sound dampening. Water-repellent (does not absorb moisture). Does not sag or settle. Denser and more rigid than fiberglass (stays in place).

Cons: More expensive than fiberglass. Heavier (harder to handle). Fewer size options than fiberglass. Not as widely available.

Comparison and Recommendations

By application: Attic floor (over joists): blown fiberglass or cellulose (most cost-effective). Attic rafter/cathedral ceiling: closed-cell spray foam or rigid foam boards. Exterior walls (new construction): fiberglass batts, mineral wool batts, or spray foam. Exterior walls (retrofit, no removal): dense-pack cellulose or injection foam. Basement walls: rigid foam board (XPS or polyiso) or closed-cell spray foam. Crawl space: closed-cell spray foam (walls) or fiberglass batts (floor joists). Rim joists: closed-cell spray foam (best air sealing). Sound insulation: mineral wool batts (best).

Cost per R-value: Fiberglass batts: cheapest per R-value. Cellulose: close second. Mineral wool: moderate. Spray foam (open-cell): moderate to high. Spray foam (closed-cell): most expensive per R-value — but doubles as air barrier.

Code minimums (IRC 2021): Climate Zone 1-2: R-13 walls, R-30 attic. Climate Zone 3: R-20 walls, R-30 attic. Climate Zone 4: R-20 walls, R-49 attic. Climate Zone 5-8: R-20+5ci walls, R-49 attic. (ci = continuous insulation on exterior).