Types of Insulation: A Homeowner's Comparison Guide

Choosing the right insulation type depends on where it's being installed, your budget, and your performance goals. Here's a straightforward comparison of the most common options.

R-Value: The Key Metric

R-value measures thermal resistance — the higher the number, the better the insulation. Every climate zone has recommended R-values. In cold climates (zones 5–7), attics typically need R-49 to R-60. In moderate climates (zones 3–4), R-38 is common.

Fiberglass Batts

Best for: Walls, floors, and attics with standard stud or joist spacing

Fiberglass batts are the most familiar type — the pink or yellow rolls you've likely seen. They're affordable and DIY-friendly, but they must fit snugly to work properly. Gaps, compression, or improper installation dramatically reduce their effectiveness.

• R-value: ~R-3.1 per inch
• Cost: $0.30–$0.65 per square foot installed
• Pros: Inexpensive, widely available, easy to work with
• Cons: Doesn't stop air movement, installation quality matters a lot

Blown-In Cellulose

Best for: Attic floors, existing walls via drill-and-fill

Cellulose is made from recycled paper treated with fire retardant. It's blown in as loose fill and conforms to irregular spaces well. It's a good choice for retrofitting existing walls without major demolition.

• R-value: ~R-3.7 per inch
• Cost: $1.00–$1.50 per square foot installed
• Pros: Good at filling gaps, eco-friendly, good cost-to-R-value ratio
• Cons: Can settle over time (reducing R-value), absorbs moisture if not properly protected

Blown-In Fiberglass

Best for: Attic floors, similar applications to cellulose

Similar to cellulose in application but made of glass fibers. Doesn't settle as much as cellulose and is moisture-resistant, but costs slightly more.

• R-value: ~R-2.5 per inch
• Cost: $1.00–$2.00 per square foot installed

Spray Foam (Open-Cell vs. Closed-Cell)

Best for: Rim joists, cathedral ceilings, tight spaces, anywhere air sealing is critical

Spray foam expands after application and adheres to surfaces, making it an excellent air barrier in addition to insulation.

Open-cell is softer, less expensive, and vapor-permeable. Good for interior applications.

• R-value: ~R-3.7 per inch
• Cost: $1.00–$2.00 per square foot

Closed-cell is denser, rigid, and acts as a vapor barrier. Best for exterior-facing surfaces or spaces prone to moisture.

• R-value: ~R-6.5 per inch (the highest of any common type)
• Cost: $2.00–$4.00 per square foot

Spray foam's air sealing properties make it a natural complement to a whole-house air sealing strategy. Learn more in What Is Air Sealing and Why Does It Matter?.

Rigid Foam Board

Best for: Basement walls, exterior sheathing, under slabs

Rigid foam panels come in three types: EPS (expanded polystyrene), XPS (extruded polystyrene), and polyisocyanurate. They're commonly used in basement wall systems and as continuous exterior insulation.

• R-value: R-3.8 to R-6.5 per inch depending on type
• Cost: $0.25–$0.65 per square foot (materials only, installation varies)

What to Ask Your Contractor

• "What R-value are you targeting and does it meet code for my climate zone?"
• "How are you addressing air sealing in addition to insulation?"
• "What's the expected settled R-value, not just the installed R-value?"
• "Are you using any rebates from my utility company?"

Frequently Asked Questions

What is the best insulation for a house? There's no single best insulation — it depends on where it's being installed and what you're trying to achieve. For attics, blown-in cellulose or fiberglass offers good coverage at reasonable cost. For rim joists and cathedral ceilings where air sealing is critical, closed-cell spray foam is hard to beat. For walls in new construction, fiberglass batts or blown-in are most common. The best approach for most homes combines multiple types in different locations.

What is the cheapest insulation with the highest R-value? Closed-cell spray foam has the highest R-value per inch at around R-6.5, but it's also the most expensive. For the best cost-to-R-value ratio, blown-in cellulose is a strong choice — it provides around R-3.7 per inch at a moderate installed cost and performs well in attics and existing walls.

Should I use spray foam or fiberglass batts? They serve different purposes. Fiberglass batts are cost-effective for walls and attic floors with standard framing, but they don't stop air movement. Spray foam costs more but acts as both insulation and an air barrier, making it the better choice for rim joists, cathedral ceilings, and any area where air sealing is as important as thermal resistance. Many contractors use both — batts for broad coverage and spray foam in critical areas.