Home Insulation Types:
Which Is Right for Your House?

Proper insulation is one of the highest-return investments in home improvement — reducing heating and cooling costs by 10–50%, improving comfort, and qualifying for federal tax credits. But with five major insulation types each suited to different applications, choosing the right one means understanding what you're actually trying to accomplish. This guide covers every major insulation type, where it works best, and what it costs in 2026.

R-Value: The Foundation of Insulation Selection

R-value measures thermal resistance — how well a material resists heat flow. Higher R-value means better insulation. What you need depends on your climate zone and where you're insulating. The DOE recommends these targets for existing homes in mixed climates (Zones 3–4, covering much of the US):

• Attic floor: R-38 to R-60
• Exterior walls: R-13 to R-21
• Crawlspace/basement walls: R-19 to R-25
• Rim joists: R-15 minimum

Use the DOE's ZIP Code Insulation Calculator (available at energysaver.gov) to get recommendations specific to your location.

Type 1: Fiberglass Batts and Rolls

R-value per inch: R-3.1 to R-4.3 | Common forms: 3.5" (R-13/15) for 2x4 walls; 5.5" (R-19/21) for 2x6 walls

The pink or yellow fluffy batts in every home improvement store. Fiberglass batts are the most common insulation in American residential construction because they're inexpensive and easy to install in standard framing during new construction.

Best Uses

• New construction wall cavities (most cost-effective for standard stud framing)
• Open attic floor between joists when adding insulation
• Accessible crawlspace joist bays

Key Limitations

• Not an air barrier: Air moves through fiberglass batts freely. In a leaky home, this dramatically reduces real-world performance vs. rated R-value.
• Must be properly fitted (no gaps, no compression) to achieve rated R-value — installation quality matters enormously
• Loses performance when wet; not suitable for high-moisture applications

Cost installed: $0.75–$1.50 per sq ft. Least expensive insulation type for standard wall applications.

Type 2: Blown-In (Cellulose or Loose-Fill Fiberglass)

R-value per inch: Cellulose: R-3.2–R-3.8 | Blown fiberglass: R-2.2–R-2.7

Loose-fill insulation blown in with a machine. Cellulose is made from recycled newspaper treated with fire-retardant boric acid. Both types are blown into open attic spaces or dense-packed into enclosed wall cavities through small holes.

Best Uses

• Attic retrofits: The go-to choice for adding insulation to existing attics — covers irregular surfaces, fills around obstructions, adds over existing insulation easily
• Dense-pack wall retrofits: Older homes with no wall insulation can be retrofitted by drilling small holes, blowing in dense-pack cellulose, and patching — far less disruptive than opening walls
• Enclosed cavities that can't accept batt insulation due to shape or accessibility

Why Cellulose Is Usually Better Than Blown Fiberglass

Higher R-value per inch, made from 80–85% recycled content, performs better in dense-pack, and has inherent pest resistance from the boric acid. Dense-pack cellulose also reduces air infiltration better than loose-fill fiberglass.

Cost installed: $1.50–$3.00 per sq ft attic; $1.50–$4.00 per sq ft for dense-pack wall (including patching). DIY attic blowing is very achievable — most home centers rent blower machines free with purchase of enough insulation bags.

Type 3: Spray Polyurethane Foam (SPF)

R-value per inch: Open-cell: ~R-3.7 | Closed-cell: R-6 to R-7

Two-part chemical foam applied wet that expands and cures rigid. Open-cell foam is soft, vapor-permeable, and lower density. Closed-cell foam is dense, rigid, and acts as a vapor barrier. Closed-cell spray foam has the highest R-value per inch of any common insulation.

Best Uses

• Rim joists and band joists: The most cost-effective spray foam application. The rim joist is one of the biggest air leak points in most homes. 2–3" of closed-cell foam here provides both high R-value and complete air sealing in one step.
• Unvented (hot roof) attic assemblies: Spraying the underside of roof decking with closed-cell foam creates a conditioned attic — excellent for homes with HVAC equipment or ductwork in the attic
• Crawlspace encapsulation: Spraying crawlspace walls and supporting the ground cover creates a conditioned crawlspace that dramatically reduces moisture issues
• Air-sealing around penetrations (pipes, wires) where canned foam works perfectly

Limitations

• Most expensive insulation type (3–5x cost of fiberglass batts)
• Professional installation required for two-part foam; improper mixing causes permanently defective product
• Occupants should vacate 24–48 hours after installation during curing
• Not easily removable — accessing walled cavities later requires mechanical removal

Cost installed: Open-cell: $0.50–$1.00 per board foot | Closed-cell: $1.00–$2.00 per board foot. Rim joist encapsulation for a typical house: $500–$1,500.

Type 4: Rigid Foam Boards

R-value per inch: EPS (white): R-3.6–R-4.2 | XPS (blue/pink board): R-5 | Polyiso: R-6–R-6.5

Rigid panels cut to size and installed in cavities or on surfaces. Three main materials: expanded polystyrene (EPS, white and beady), extruded polystyrene (XPS, the familiar blue or pink boards), and polyisocyanurate (polyiso, foil-faced).

Best Uses

• Basement walls: Rigid foam adhered directly to concrete or masonry walls, then covered with framing and drywall — effective basement thermal and moisture control
• Exterior continuous insulation: Adding rigid foam over exterior sheathing before new siding goes on eliminates thermal bridging through wall studs — highly effective but usually done only during re-siding projects
• Under-slab insulation: EPS under concrete slabs significantly reduces energy loss through the foundation
• Attic hatch covers: Gluing rigid foam to the back of an attic hatch is a simple, effective upgrade
• Knee walls in finished attics: Where batts don't fit well, rigid foam panels can line knee wall spaces

Cost installed: $1.50–$3.00 per sq ft depending on thickness and R-value target. Can be DIY for accessible applications like basement walls.

Type 5: Mineral Wool (Rock Wool / Slag Wool)

R-value per inch: R-3.0 to R-3.3 | Common brands: Rockwool Comfortbatt, Thermafiber

Made from volcanic rock (basalt) or blast furnace slag spun into fibers. Mineral wool is the premium batt insulation with several advantages over fiberglass batts, though at a 20–40% cost premium.

Advantages Over Fiberglass Batts

• Fire resistance: Mineral wool is naturally fire-resistant to over 2,000°F — used in fire-rated assemblies. Fiberglass melts at much lower temperatures.
• Water resistance: Mineral wool repels water (doesn't absorb moisture) and maintains R-value when damp. Excellent for exterior applications and high-humidity areas.
• Acoustic performance: Denser than fiberglass, mineral wool provides significantly better sound attenuation. Used extensively in interior partition walls for sound control (between bedrooms, home theater rooms, home offices).
• Rigidity: Mineral wool batts are stiffer and hold their shape better during installation, making it easier to achieve proper fit without gaps or compression.
• Air resistance: Denser structure provides marginally better air resistance than fiberglass batts (though still not an air barrier).

Best Uses

• Interior sound-control walls (home theaters, bedrooms, office partitions)
• Fire-rated wall and floor assemblies
• Exterior walls in high-humidity climates or where moisture intrusion risk exists
• Any application where fiberglass batts work, with better performance

Cost installed: $1.00–$2.50 per sq ft (20–40% premium over fiberglass batts).

Which Insulation Type Should You Choose?

Don't Forget Air Sealing

The most important insight in building science: air sealing before or alongside insulation matters as much as the insulation itself. In a typical existing home, air infiltration through gaps, penetrations, and bypasses accounts for 25–40% of heating and cooling costs. Blown-in cellulose and spray foam provide some air sealing; fiberglass batts do not.

Before adding any insulation to an attic, a professional energy auditor or insulation contractor should air-seal top-plate penetrations (where interior walls meet the attic floor), recessed light cans (a major heat bypass), plumbing and wiring penetrations, and the attic hatch. This step is often more impactful than the insulation itself in older homes.

Federal Tax Credits for Insulation (2026)

The Inflation Reduction Act's Energy Efficient Home Improvement Credit (25C) provides a tax credit of 30% of the cost of qualifying insulation, up to $1,200 per year. This applies to insulation installed in existing homes (not new construction). Consult your tax advisor for specifics. Many state and local utility programs also offer rebates for insulation improvements — check your utility company's website.

For more on home improvement projects that affect energy efficiency, our weatherstripping guide for doors and windows covers another high-impact air sealing project. And our spring home maintenance checklist includes an attic inspection item that can help you assess your current insulation level.