Best Insulation Types for Your Home: R-Value Guide

Understanding R-Value

R-value measures an insulation material's resistance to heat flow. Higher R-values mean better insulating performance. R-value is additive, so two layers of R-10 insulation provide R-20. However, R-value alone does not tell the whole story. Air sealing, moisture management, and proper installation are equally important. Poorly installed R-38 batts with gaps and compression can perform worse than well-installed R-30.

The 2021 International Energy Conservation Code (IECC), which most jurisdictions have adopted or exceeded by 2026, sets minimum R-value requirements based on climate zone. These minimums represent the floor, not the ceiling. In many cases, exceeding code requirements by R-10 to R-20 in the attic pays for itself in energy savings within 3 to 5 years.

R-Value Requirements by Climate Zone

Use our insulation calculator to determine exactly how much insulation you need based on your climate zone and the area you are insulating. The calculator accounts for R-value requirements and provides material quantity estimates.

Fiberglass Batts and Rolls

Fiberglass batts remain the most widely used insulation in residential construction. They are inexpensive, widely available, and easy to install in standard framing cavities. Standard batts deliver R-3.2 to R-3.8 per inch. A 3.5-inch batt (for 2x4 walls) provides R-11 to R-13. A 5.5-inch batt (for 2x6 walls) provides R-19 to R-21.

Installed cost runs $0.50 to $1.50 per square foot, making fiberglass the cheapest option. The major downside is that batts do not air-seal, and even small gaps reduce performance dramatically. A 5 percent gap in coverage can reduce effective R-value by 25 percent. Fiberglass also loses performance when compressed. Never stuff R-19 batts into a 2x4 cavity, as you will get roughly R-12 with increased air leakage. Fiberglass batts are best for open walls during new construction and standard attic insulation over flat ceilings.

Blown-In Cellulose

Cellulose insulation is made from recycled newspaper treated with borates for fire and pest resistance. It delivers R-3.5 to R-3.7 per inch and costs $0.80 to $1.50 per square foot installed. Cellulose is the go-to choice for retrofitting existing walls because it can be dense-packed into closed cavities through 2-inch holes drilled in the exterior or interior.

Dense-pack cellulose at 3.5 pounds per cubic foot provides both insulation and significant air sealing, unlike fiberglass batts. In attics, loose-fill cellulose blown to a depth of 10 to 14 inches achieves R-38 to R-49. The material settles 10 to 15 percent over time, so installers compensate by over-blowing. Cellulose handles moisture better than fiberglass because borate-treated cellulose absorbs and releases moisture without losing R-value.

Closed-Cell Spray Foam

Closed-cell spray foam (ccSPF) delivers the highest R-value per inch at R-6 to R-7. It also serves as an air barrier, vapor retarder, and structural reinforcement. At 2 inches thick, it provides R-13 plus airtight sealing. At 3 inches, it delivers R-20. Installed cost runs $1.50 to $3.50 per square foot per inch of thickness, making a 3-inch application $4.50 to $10.50 per square foot.

Closed-cell spray foam is the premium choice for rim joists, crawl spaces, cathedral ceilings, and any location where you need maximum R-value in limited depth. It is also the best option for flood-prone areas because it does not absorb water. The downsides are cost (2 to 3 times more than alternatives), the need for professional installation with specialized equipment, and potential off-gassing during application that requires vacating the building for 24 hours.

Open-Cell Spray Foam

Open-cell spray foam (ocSPF) provides R-3.5 to R-3.8 per inch at roughly half the cost of closed-cell, running $0.75 to $1.50 per square foot per inch. It expands aggressively to fill every crack and crevice, providing excellent air sealing. A 5.5-inch application in a 2x6 wall delivers R-19 to R-21 with a complete air seal.

Open-cell foam is vapor-permeable, meaning it allows walls to dry in both directions. This makes it suitable for warm and mixed climates but risky in cold climates (zones 6-7) where interior moisture could condense within the wall assembly. It absorbs water, so it is not appropriate for below-grade applications. Open-cell foam is ideal for interior walls (soundproofing), attic rooflines in mixed climates, and anywhere you want air sealing without the cost of closed-cell.

Mineral Wool (Rockwool)

Mineral wool batts deliver R-3.8 to R-4.2 per inch, slightly better than fiberglass. A 3.5-inch batt provides R-15 (versus R-13 for fiberglass of the same thickness). Installed cost runs $1.00 to $2.50 per square foot. Mineral wool is naturally fire-resistant, repels water, and provides excellent sound attenuation.

Mineral wool batts are denser and more rigid than fiberglass, which makes them easier to friction-fit without sagging. They hold their shape better around pipes and wires. Mineral wool is increasingly popular for exterior continuous insulation in the form of rigid boards (like Rockwool Comfortboard), which wrap the outside of the sheathing to break thermal bridges at studs. Use mineral wool in fire-prone areas, as sound barriers between rooms, and as exterior continuous insulation.

Rigid Foam Board

Rigid foam boards come in three types: expanded polystyrene (EPS, R-3.8 per inch), extruded polystyrene (XPS, R-5 per inch), and polyisocyanurate (polyiso, R-5.7 to R-6.5 per inch). Installed costs range from $1.00 to $3.00 per square foot depending on type and thickness. Rigid foam is essential for foundation insulation, below-grade applications, and exterior continuous insulation.

XPS (pink or blue boards) is the standard for below-grade foundation insulation because it resists moisture absorption. Polyiso delivers the highest R-value per inch but loses performance in cold temperatures below 50 degrees Fahrenheit, making it better suited for above-grade exterior walls and roofing. EPS is the most affordable option for insulated concrete forms (ICFs) and structural insulated panels (SIPs). Rigid foam should be sealed at all joints with tape or canned foam to function as an air barrier.

Insulation Cost Comparison

Best Insulation by Application

Attics

For unfinished attics with a flat ceiling, blown-in cellulose or fiberglass is the most cost-effective option. Blow to a minimum of R-49 in climate zones 4 and above. Air-seal all penetrations (light fixtures, plumbing vents, electrical boxes, top plates) before adding insulation. For cathedral ceilings, closed-cell spray foam against the roof deck is the best performer, though it costs significantly more.

Exterior Walls

In new construction, fill the cavity with fiberglass or mineral wool batts and add continuous exterior insulation (rigid foam or mineral wool board) to break thermal bridging at studs. For existing walls, dense-pack cellulose blown through small holes is the least disruptive retrofit. Our drywall calculator can help you estimate materials if you need to repair or replace drywall after insulation work.

Basements and Crawl Spaces

For basement walls, use XPS rigid foam (R-10 to R-15) adhered directly to the concrete, then frame a 2x4 wall in front with optional additional insulation. Never use fiberglass batts against concrete because they absorb moisture and grow mold. For crawl spaces, closed-cell spray foam on the rim joist and foundation walls is the gold standard. Encapsulate the crawl space with a 20-mil vapor barrier on the floor.

DIY vs. Professional Installation

Fiberglass batts and rigid foam boards are straightforward DIY projects. Blown-in cellulose can be DIY with a rented blowing machine (free from most big-box stores with material purchase), though professional installation is more consistent. Spray foam, both open and closed cell, requires professional installation with specialized equipment. Attempting DIY spray foam with canned products produces inconsistent results and is only practical for small gaps and penetrations.

For advice on which insulation projects you can handle yourself and which require a contractor, read our DIY vs. contractor guide. When insulation is part of a larger energy retrofit, JouleIO's energy calculators can help you model expected savings.

Tax Credits and Incentives for 2026

The Inflation Reduction Act provides a federal tax credit of 30 percent of insulation material costs (up to $1,200 per year) for qualifying improvements installed in your primary residence. Qualifying insulation includes batts, rolls, blown-in, spray foam, and rigid boards that meet or exceed IECC standards for your climate zone. The credit covers material costs but not labor.

Many utilities offer additional rebates of $0.10 to $0.25 per square foot for attic insulation upgrades and $200 to $500 for air sealing. Check with your local utility or visit the DSIRE database for available incentives in your area. If you are financing energy improvements, Amortio's loan calculator can help you estimate monthly payments on a home improvement loan.

Frequently Asked Questions