Insulation R-Value Chart: Complete Guide to Every Material (2026)

Quick Answer: R-value measures insulation's resistance to heat flow — higher numbers mean better insulating performance. Closed-cell spray foam tops the chart at R-6.0 to R-7.0 per inch, while standard fiberglass batts deliver R-3.0 to R-3.7 per inch. Most homes need R-49 to R-60 in the attic, R-13 to R-23 in walls, and R-13 to R-38 in floors, depending on climate zone.

Table of Contents

• Complete R-Value Insulation Chart
• R-Value Requirements by Location
• How to Read This Chart
• R-Value by Application: What Goes Where
• Why R-Value Isn't Everything
• Temperature Effects on R-Value
• Common Mistakes
• Key Takeaways
• FAQ

---

Complete R-Value Insulation Chart

We've installed every material on this list — in attics where it's 140°F in July and crawl spaces where you're on your belly in standing water. This chart reflects real-world performance, not just what the manufacturer prints on the bag.

Costs are 2025–2026 national averages, professionally installed. Rigid foam board costs are material-only — installation adds $0.50–$1.50/sq ft depending on application. R-value data sourced from manufacturer spec sheets (Owens Corning product catalog, Rockwool Comfortbatt technical data). See our insulation cost calculator for project-specific pricing.

Pro Tip: Don't pick insulation by R-value per inch alone. Blown-in fiberglass has the lowest R-per-inch on this chart but it's one of the most cost-effective choices for open attics because you can pile it as deep as you need. At 16–18 inches, it hits R-38 to R-49 for $1.00–$2.00/sq ft installed.

---

R-Value Requirements by Location

The 2021 International Energy Conservation Code (IECC) sets minimum R-values by climate zone. Your local jurisdiction may adopt these directly or modify them — check with your building department, as some states lag 1–2 code cycles behind. The DOE's insulation guidance page provides federal recommendations by ZIP code, and Energy Star's Seal and Insulate guide covers retrofit priorities.

2021 IECC Minimum R-Value Requirements

"ci" = continuous insulation — rigid foam or spray foam applied over the exterior of the framing to reduce thermal bridging. "R-13+5ci" means R-13 cavity insulation plus R-5 of continuous exterior insulation.

Energy Star Retrofit Recommendations

Already have some insulation? Energy Star provides separate guidance for adding to existing insulation vs. starting from scratch:

Use our climate zone map to find your zone, then reference the code requirements page for your state-specific amendments.

Pro Tip: Code is a minimum. Going above code — especially in the attic — almost always pays for itself inside 3–5 years. The DOE estimates that upgrading from R-19 to R-49 in a 1,500 sq ft attic saves $200–$400 per year on heating and cooling. That's a 2–4 year payback on a $600–$1,200 job.

---

How to Read This Chart

If you're new to insulation, the chart above can look overwhelming. Here's what the numbers actually mean.

R-value per inch is a rate — how much thermal resistance one inch of the material provides. This is how you compare materials on an apples-to-apples basis. See our R-value per inch chart for a deep-dive ranking.

Total R-value is what actually matters for your building. It's R-per-inch multiplied by the thickness you install. A 2×4 wall cavity is 3.5 inches deep, so standard fiberglass batt (~R-3.14 per inch) delivers about R-11 in that cavity. A 2×6 wall at 5.5 inches deep gives you R-19. Simple multiplication.

Installed cost per square foot reflects what you'll actually pay a contractor in 2025–2026, including labor and material. Material-only costs for rigid foam boards are noted separately since installation varies widely (gluing to a foundation wall vs. mechanically fastening over exterior sheathing).

R-values add up across layers. A wall assembly with R-13 cavity insulation, R-5 continuous exterior foam, R-0.45 for drywall, R-0.63 for sheathing, and R-0.85 for air films totals approximately R-20 for the assembly. Our R-value calculator does this math for you, and ORNL's whole-wall R-value calculator provides lab-validated assembly performance data.

For a full explanation of what R-value means and the physics behind it, see What Is R-Value?.

---

R-Value by Application: What Goes Where

Not every material works in every location. Here's what we install most often — and why — for each part of the house.

Attic (Flat Ceiling / Attic Floor)

Target: R-49 to R-60 (climate zones 4–8)

Best options: blown-in cellulose or blown-in fiberglass to the required depth. At R-3.5 per inch, cellulose needs ~14 inches for R-49 and ~17 inches for R-60. Blown-in fiberglass at R-2.5/inch needs ~20 inches for R-49, but the material cost is comparable.

For a 1,500 sq ft attic floor, expect $1,000–$2,500 installed with blown-in material. See our attic insulation cost guide for detailed pricing.

Walls (New Construction)

Target: R-13 to R-23 (depending on zone)

Standard approach: fiberglass or mineral wool batts in the stud cavity, plus continuous rigid foam on the exterior in zones 5+. A 2×6 wall with R-21 high-density fiberglass batt plus R-5 polyiso on the exterior delivers a whole-wall R-value around R-22 — well above code for most zones.

Walls (Retrofit)

Target: Match the cavity (typically R-13 in 2×4, R-19 to R-21 in 2×6)

Best option: dense-pack cellulose blown in through small holes drilled in the siding or interior plaster. At R-3.5–R-3.8 per inch, it fills a 2×4 cavity to about R-13, plus it provides excellent air-sealing properties. Read our wall insulation guide for the full retrofit process.

Basement Walls

Target: R-10ci to R-19 (zones 4–8)

Best options: Closed-cell spray foam directly on the concrete (2–3 inches gives R-12 to R-21 and a built-in vapor barrier), or rigid foam board (XPS or EPS) with a framed wall over it. See our basement insulation guide.

Crawl Space / Floor Over Unconditioned Space

Target: R-13 to R-38 (depending on zone)

Conditioned crawl spaces: insulate the walls with rigid foam or spray foam. Unconditioned: insulate the floor above with fiberglass batts (R-19 or R-30 faced batts between floor joists) or spray foam on the underside. Check our crawl space guide for the full breakdown.

We've seen a lot of floor insulation fail — fiberglass batts sag away from the subfloor over time, creating an air gap that tanks performance. If you go the batt route, support them with insulation support wires (tiger teeth) spaced every 18 inches. Better yet, spray foam on the underside of the subfloor stays put permanently and air seals the floor assembly. For a typical 1,200 sq ft crawl space in zone 5, R-30 fiberglass batts cost roughly $600–$1,800 installed, while spray foam on the crawl space walls (the preferred approach for conditioned crawl spaces) runs $1,500–$4,000.

Roof (Cathedral Ceilings / Vaulted Ceilings)

Target: R-30 to R-49 (depending on zone and assembly type)

Cathedral ceilings are one of the hardest assemblies to insulate well because you're working within a fixed rafter depth — typically 2×8 (7.25") or 2×10 (9.25") — with no accessible attic space above. A 2×10 rafter filled with fiberglass gives you about R-30, which falls short of the R-49 or R-60 ceiling requirement in zones 4+.

Three approaches work here. First, open-cell spray foam sprayed directly on the underside of the roof deck fills the full rafter depth and air seals simultaneously — 5.5 inches in a 2×6 gives R-19 to R-21, while 9.25 inches in a 2×10 delivers R-32 to R-35. Second, a hybrid approach: closed-cell spray foam on the roof deck (2 inches for R-12 to R-14 plus air/vapor barrier) with the remaining cavity filled with dense-pack cellulose or fiberglass batt. Third, rigid foam installed above the roof deck during a re-roof, which adds R-value without eating into rafter depth — 3 inches of polyiso above the sheathing adds R-17 to R-19 (derate for cold climates).

Floor Over Garage

Target: R-19 to R-30 (match your wall requirement or higher)

The floor above an attached garage needs insulation for both energy performance and fire separation. A typical approach: R-19 or R-30 unfaced fiberglass batts between the floor joists, supported with insulation wires, plus 5/8" Type X fire-rated drywall on the garage ceiling. For better air sealing, we prefer spray foam on the underside — 2 inches of closed-cell provides R-12 to R-14 plus an air barrier, and you can fill the rest with batts to reach R-30. This assembly also helps block carbon monoxide and vehicle exhaust from migrating into the living space.

---

Why R-Value Isn't Everything

We've seen R-38 attics that perform worse than R-19 attics. The label R-value is tested in a lab at 75°F mean temperature with zero air movement, zero moisture, and perfect installation. Your house is not a lab.

Three factors that kill real-world performance:

1. Air Leakage Insulation slows conductive heat transfer. It does almost nothing to stop air carrying heat through gaps, cracks, and penetrations. The DOE estimates that air sealing alone saves 15–25% on heating and cooling. If you insulate without air sealing, you're leaving half the job undone.

2. Installation Quality RESNET grades insulation installation from Grade I (perfect fill, no gaps, no compression) to Grade III (visible gaps, voids, compression). The performance difference between Grade I and Grade III is 30% or more. A Grade III R-19 wall performs like an R-13 wall or worse. We've pulled back drywall on houses less than five years old and found fiberglass batts stuffed behind wiring and plumbing with 20% of the cavity empty.

3. Thermal Bridging Wood framing conducts heat 3–4× faster than the insulation between it. In a standard 2×6 wall framed 16 inches on center, 23–25% of the wall area is lumber. That thermal bridging drops a cavity R-23 wall to about R-18 whole-wall. The fix: continuous insulation over the framing. Adding just R-5 of exterior foam to that wall bumps the whole-wall value to ~R-19 — a 27% improvement over the R-15 you'd expect without it.

---

Temperature Effects on R-Value

Not all insulation performs the same in every climate. The FTC requires R-value testing at 75°F mean temperature, but your attic in Minnesota doesn't stay at 75°F.

Polyisocyanurate (polyiso) is the biggest offender. It's rated R-5.6 to R-6.5 per inch at 75°F but drops to R-3.5–R-4.5 per inch when the mean temperature falls below 25°F. Building Science Corporation's research on rigid foam temperature performance shows polyiso can lose up to 25% of its labeled R-value when mean temperatures drop below 50°F. If you're in zone 5 or higher and using polyiso on the exterior, derate it or layer it with XPS or EPS.

XPS foam board actually performs slightly better in cold temperatures — its R-value per inch improves slightly as temperature drops. However, XPS uses blowing agents that off-gas over time, and its long-term R-value settles closer to R-4.5 per inch.

EPS foam board is the most temperature-stable rigid foam option. Its R-value stays consistent across a wide temperature range, making it a reliable choice for below-grade and cold-climate applications.

Fiberglass and mineral wool are largely unaffected by temperature, making them predictable performers in any climate.

For a complete analysis, see our individual guides on polyiso, XPS, and EPS.

---

Common Mistakes

1. Compressing batts to fit. An R-19 batt is 6.25 inches thick. Stuffing it into a 3.5-inch 2×4 cavity doesn't give you R-19 in less space — it gives you approximately R-13. Compression reduces R-value proportionally. Use the right product for the cavity: R-13 or R-15 for 2×4, R-19 or R-21 for 2×6. See our insulation thickness chart for correct pairings.

2. Ignoring air sealing. Insulation without air sealing is like wearing a sweater with no windbreaker. Seal penetrations, top plates, recessed lights, and duct boots before insulating. Our guide on air sealing vs. insulation explains the priority order.

3. Using the wrong vapor barrier. In cold climates (zones 5+), you generally want a vapor retarder on the warm side of the insulation. In mixed or hot-humid climates, putting poly on the wrong side traps moisture and rots framing. Check our vapor barrier guide before you install faced vs. unfaced insulation.

4. Comparing materials on R-value per inch alone. Closed-cell spray foam at R-6.5/inch is impressive, but at $1.50–$5.00/sq ft it's 3–5× the cost of blown-in cellulose that gets you to the same total R-value in an open attic. Compare total R-value for your application, then compare cost. The R-value per inch chart shows the full picture.

5. Not accounting for settling. Cellulose insulation settles approximately 20% in the first few years. If you need R-49 (about 14 inches), install to 17–18 inches initially to account for settling. Good installers already do this — ask about their settled-density specifications.

---

Key Takeaways

• Closed-cell spray foam delivers the highest R-value per inch (R-6.0–R-7.0), but blown-in cellulose and fiberglass offer the best value for open spaces like attics where thickness isn't constrained.
• Most homes in zones 4–8 need R-49 to R-60 in the attic, R-20+5ci in walls, and R-19 to R-38 in floors per the 2021 IECC.
• R-value is only part of the picture — air sealing, installation quality, and thermal bridging can make or break actual performance.
• R-values add up across layers: cavity insulation + continuous insulation + sheathing + drywall + air films all contribute.
• Polyiso R-value drops significantly in cold temperatures — derate it in climate zones 5+ or pair it with EPS/XPS.
• Always match insulation thickness to cavity depth. Compressing batts wastes money and R-value.
• The DOE estimates proper insulation and air sealing reduce heating/cooling costs by 15–25%, with attic upgrades paying for themselves in 2–5 years.

---

FAQ

What R-value do I need for my home?

It depends on your climate zone and which part of the house you're insulating. The 2021 IECC requires R-49 to R-60 for attics, R-13 to R-20+5ci for walls, and R-13 to R-38 for floors, scaling with colder climates. Use our R-value calculator to determine your specific needs — enter your ZIP code, assembly type, and existing insulation to get a personalized recommendation.

Do R-values add up when you stack insulation?

Yes. R-values are additive across layers. If you have R-19 existing attic insulation and blow R-30 on top, you get R-49 total. This works across different materials too — R-13 fiberglass cavity insulation plus R-5 continuous exterior polyiso gives you R-18 of insulation, plus another R-2 or so from drywall, sheathing, and air films. See What Is R-Value? for how assemblies add up.

What insulation has the highest R-value?

Closed-cell spray foam leads at R-6.0 to R-7.0 per inch. Polyiso rigid foam is close behind at R-5.6 to R-6.5 per inch (at 75°F). For a complete ranking, see our R-value per inch chart. Keep in mind that the highest R-per-inch isn't always the best choice — it's often the most expensive, and in open spaces like attics, cheaper materials at greater thickness deliver the same total R-value for far less money.

Is higher R-value always better?

More R-value is always better at resisting heat flow, but there's a point of diminishing returns. Going from R-0 to R-19 in an attic is massive — you'll cut heat loss through the ceiling by about 95%. Going from R-19 to R-38 saves roughly half again. But going from R-38 to R-60 adds only another incremental improvement. Beyond code requirements, the payback period stretches from 2–3 years to 7–10+ years. Our recommendation: hit code minimum at least, go above in the attic if budget allows, and always prioritize air sealing first.

How thick is R-30, R-38, and R-49 insulation?

It depends on the material. Here are approximate thicknesses:

For complete thickness data across all materials, see our insulation thickness chart.