Residential insulation comes in four main categories—blankets (batts and rolls), loose-fill, spray foam, and foam board—and the right choice depends on where you are insulating and how much thermal resistance you need. Focus on Energy ranks these categories from lowest to highest R-value per inch in the order listed above, which means foam board delivers more insulation in less thickness than blanket products. Attics generally call for higher R-values than walls: a commonly cited target is R-23 for exterior walls, while attics may call for R-30, R-38, or R-49, with R-49 or higher considered best. This guide compares the categories and maps them to those targets.
Understanding R-Value: The Key to Insulation Performance
R-value measures an insulation material's resistance to heat flow, and according to Focus on Energy, it depends on the type, thickness, and density of the material, as well as the temperature, moisture levels, and age of the insulated space. Generally, the higher the rating, the higher the performance—though the source cautions that rating alone does not determine how effective insulation will be in a given space. If you install new insulation over an existing layer, all of those factors contribute to the overall R-value of the assembly.
It also helps to know the two primary installation approaches described by the Southeast Energy Efficiency Alliance: continuous insulation, which spans across structures without interruptions and is commonly installed on the exterior of the home, and cavity insulation, which fills the spaces between framing members. Foam board is often associated with continuous applications, while batts, loose-fill, and spray foam typically fill cavities.
Blanket Insulation: Batts and Rolls
Blanket insulation comes as batts and rolls, and fiberglass is a common material for this category, with mineral wool also available. According to an R-value chart attributed to the U.S. Department of Energy and distributed by Oncor, fiberglass batts provide an R-value of about 3.1 per inch, with rockwool batts at roughly 3.2. That places blankets at the lower end of the per-inch performance range among the four categories.
ENERGY STAR notes that different insulation types require varying degrees of skill to install, which can help you decide whether to hire a contractor or take on the project yourself. Blanket products are the form most homeowners picture when they think of insulation, and their pre-cut form makes them a familiar option for framed cavities. Greenfiber, a cellulose manufacturer, states that its blow-in product outperforms fiberglass batting per inch, which is consistent with the per-inch figures above.
Loose-Fill Insulation: Blown-In Options
Loose-fill insulation consists of materials such as cellulose, fiberglass, or mineral wool that are blown into cavities using specialized equipment. Per-inch figures vary by product and density: the Oncor-distributed chart lists blown fiberglass at 2.2 to 2.8 per inch depending on the product, while blown cellulose for attics is listed at 3.7. Greenfiber states its SANCTUARY cellulose delivers 3.7 per inch.
The blown-in method makes loose-fill suitable for irregular spaces and existing walls, where fitting blankets would be impractical. Attics are a natural fit: Greenfiber's calculator guidance says that to reach an attic R-value of 38 to 49, you should aim for 11 to 14 inches of blow-in cellulose, depending on your climate zone and needs. That thickness requirement illustrates the practical trade-off of a mid-range per-inch material.
Spray Foam Insulation: Sealing and Insulating
Spray foam insulation, available in open-cell and closed-cell types, expands to fill cavities and can be applied in various densities. It differs from the other categories by combining insulation with air sealing in a single applied product. Per-inch performance splits sharply by type: the Oncor-distributed chart lists open-cell spray foam at 3.5 per inch and closed-cell at 6.2, while Efficiency Manitoba's generic chart for unknown manufacturers covers spray polyurethane foam among its materials.
Closed-cell foam generally provides higher thermal resistance per inch than open-cell, which matters when cavity depth is limited. Green Builder Media's buyer guide discusses spray foam in the context of cavity space and air sealing, noting that building codes require a certain amount of insulation in every new home and that some builders aim beyond code minimums toward net-zero performance.
Foam Board Insulation: Rigid and Efficient
Foam board is the rigid category, and Focus on Energy places it highest among the four in R-value per inch. The Oncor-distributed chart lists polystyrene board at 4.0 per inch and polyurethane board at 6.0, while Efficiency Manitoba's chart distinguishes expanded polystyrene, extruded polystyrene, and polyisocyanurate board products. Because rigid boards can span framing without interruption, they align with the continuous-insulation approach described by the Southeast Energy Efficiency Alliance.
This is why foam board often appears as insulative wall sheathing rather than cavity fill. ENERGY STAR's recommended R-values, based on the 2021 International Energy Conservation Code (IECC) Residential Provisions Table R402.1.3, repeatedly call for insulative wall sheathing—for example, adding R-10 sheathing beneath new siding for insulated 2x4 wood-frame walls in Zones 4–8, or R-5 to R-15 sheathing options for basement and crawlspace walls depending on zone.
Insulation Type Comparison Chart
The table below categorizes the common insulation materials by form and relative thermal resistance per inch, using the sourced classifications and figures. Use it to see at a glance which categories deliver higher R-value in less space and how each form dictates its use.
| Insulation Category | Common Forms | Relative R-Value (Per Inch) | Typical Installation Method |
|---|---|---|---|
| Blanket insulation | Fiberglass or mineral wool batts and rolls | Lower end: fiberglass batt ~3.1; rockwool batt ~3.2 | Fitted into framed cavities; skill level varies by project |
| Loose-fill insulation | Blown cellulose, blown fiberglass, blown mineral wool | Mid-range: blown fiberglass 2.2–2.8; blown cellulose ~3.7 (varies by product and density) | Blown into attics or wall cavities with specialized equipment; suits irregular spaces and existing walls |
| Spray foam insulation | Open-cell and closed-cell applied foam | Open-cell ~3.5; closed-cell ~6.2–6.5 (varies by density) | Sprayed into cavities, expanding to fill and seal air leaks |
| Foam board insulation | Rigid polystyrene, polyurethane, and polyisocyanurate boards | Highest of the four: polystyrene ~4.0; polyurethane ~6.0 | Installed as rigid panels, often as continuous wall sheathing |
The pattern is clear: moving from blankets to foam board generally buys more R-value per inch of thickness, while the form factor—batt, blown, sprayed, or rigid panel—determines where each product can physically go.
Matching Insulation to Home Areas: Attics and Walls
Higher R-values are generally recommended for attics than walls, and the reasoning is thermal: LearnMetrics' R-value chart, hosted in a Permies forum attachment, explains that high values (R-40 or more) make sense for places over your head because hot air leaves the house there in winter and sun strikes those surfaces in summer. A good R-value for exterior walls is R-23, while attics and ceilings can range from R-30 to R-49, with R-49 considered best for attics.
ENERGY STAR's formal recommendations, drawn from the 2021 IECC, vary by climate zone—for instance, basement and crawlspace wall guidance ranges from R-5 sheathing or an R-13 batt in Zone 3 up to R-15 sheathing or an R-19 batt in Zones 4C and 5–8. These figures are illustrative; actual requirements depend on your specific climate zone, and local building codes must be verified separately. In practice, deep attic targets favor loose-fill cellulose (11 to 14 inches reaches R-38 to R-49 per Greenfiber), while limited wall-cavity depth favors closed-cell spray foam or foam board sheathing to reach wall targets in less thickness.
Making an Informed Insulation Choice
Homeowners and contractors should select insulation based on the specific area of the building, considering the required R-value for their climate zone and the insulation's form factor and installation method. Start by identifying the target R-value for the location—roughly R-23 for walls versus R-30 to R-49 for attics, per the cited charts—then check whether your cavity depth, at the per-inch figures in the comparison table, can reach that target, and whether the installation method suits a DIY approach or a contractor.
After installation, the measurable indicator of success is straightforward: the project's energy bills show a measurable reduction, indicating improved thermal performance. Track heating and cooling costs across a full season against pre-insulation bills for the same period, and note that this article compares broad categories rather than specific brands, excludes cost estimates, and does not address local code requirements you must verify for your location.
Sources
- Understanding R-Values and Insulation — Focus on Energy
- Why We Should Insulate Homes - Southeast Energy Efficiency Alliance
- ONCOR
- Choosing the Appropriate Insulation Type — ENERGY STAR
- Blown-In Insulation Calculator to Estimate Costs — Greenfiber
- Efficiencymb
- Insulation R-Values Chart and Buyer Guide — Greenbuildermedia
- Recommended Home Insulation R–Values — ENERGY STAR
- Permies
