Estimate R-value, insulation thickness & project cost in seconds. Trusted by homeowners and contractors across the US in 2026.
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Choose whether you're insulating an attic, wall, floor, basement, or cathedral ceiling.
Your US climate zone determines the DOE's recommended R-value targets for 2026.
Select from 8 popular materials, each with real R-value per inch ratings used in the calculation.
Instantly see R-value, thickness needed, material cost, installed cost, and energy savings.
Quick reference for all 8 insulation materials covered by our calculator.
| Insulation Type | R-Value / Inch | Best For | Cost Range (per sq ft) |
|---|---|---|---|
| Fiberglass Batt | 2.2 – 2.7 | Walls, Attics | $0.30 – $1.00 |
| Blown-In Cellulose | 3.2 – 3.8 | Attics, Walls | $0.50 – $1.50 |
| Open-Cell Spray Foam | 3.5 – 3.7 | Walls, Crawl Spaces | $0.44 – $0.65 |
| Closed-Cell Spray Foam | 6.0 – 7.0 | Roofs, Foundations | $1.00 – $2.00 |
| Mineral / Rock Wool | 3.0 – 3.3 | Walls, Fire Resistance | $0.80 – $1.50 |
| Rigid Foam – EPS | 3.6 – 4.2 | Foundations, Roofs | $0.25 – $0.50 |
| Rigid Foam – XPS | 5.0 | Basements, Below Grade | $0.40 – $0.70 |
| Rigid Foam – Polyiso | 5.6 – 8.0 | Roofs, Walls | $0.45 – $0.80 |
R-value measures how well insulation resists heat flow. Higher R-value means better insulation. In 2026, the DOE recommends specific R-values by climate zone to maximise energy efficiency and reduce heating/cooling bills year-round.
Most US attics need R-38 to R-60 depending on your climate zone. Southern zones require R-38, while colder northern zones need R-49 to R-60. Use the calculator above for a precise recommendation for your zone.
Closed-cell spray foam and mineral wool are top-rated for exterior walls in 2026 due to high R-value per inch and excellent moisture resistance. Fiberglass batt remains the most popular budget-friendly option for standard wall cavities.
Our calculator uses DOE climate zone recommendations and industry-standard R-value data updated for 2026. Actual costs may vary based on contractor rates and local market conditions — use it as a reliable project planning baseline.
Yes, in most cases you can layer new insulation over existing. Enter your current R-value into the calculator and it will calculate exactly how much additional insulation you need to reach the 2026 DOE-recommended target for your zone.
Everything you need to know about insulation types, R-values, climate zones, and how to save money on energy bills this year.
Read the 2026 Guide →