Insulation Types at a Glance: Batts, Blown-In, Spray Foam, and Rigid Board

Why Insulation Type Matters

Insulation is one of the most impactful improvements you can make to a home's thermal envelope — the boundary that separates conditioned indoor air from the outdoors. Choosing the right material depends on where it's being installed, your budget, and the R-value your climate zone requires.

R-value measures thermal resistance: the higher the number, the better the material resists heat flow. But R-value isn't the only factor. Some insulation types also block air movement or manage moisture, which affects real-world performance. For a broader look at how insulation fits into home energy upgrades, see our guide to energy efficiency upgrades.

The Four Main Residential Insulation Types

Batt Insulation

Batts are pre-cut rectangular sections of fibrous material — typically fiberglass or mineral wool — sized to fit standard stud and joist spacing (16 or 24 inches on center). They are the most widely recognized insulation format and are suited to open wall cavities, floors above unheated spaces, and attic floors during new construction or gut renovations.

• Typical R-value: R-3.1 to R-4.3 per inch, depending on material
• Best uses: Interior walls, wood-framed floors, attic floors with open joists
• Limitations: Must be installed without gaps or compression; poor fit around obstructions reduces effectiveness significantly

Blown-In (Loose-Fill) Insulation

Blown-in insulation consists of loose fibers or granules — cellulose, fiberglass, or mineral wool — pneumatically blown into place using specialized equipment. It conforms to irregular spaces and can be added over existing insulation, making it a practical retrofit choice for attics. See our deep-dive on attic insulation performance and R-values for additional context.

• Typical R-value: R-2.2 to R-3.8 per inch
• Best uses: Attic floors, existing wall cavities (dense-pack method), hard-to-reach spaces
• Limitations: Can settle over time, reducing effective R-value; requires rented or hired equipment

Spray Foam Insulation

Spray polyurethane foam (SPF) expands on contact to fill cavities and seal air gaps simultaneously. It comes in two formulations: open-cell (softer, lower R-value, vapor-permeable) and closed-cell (rigid, higher R-value, acts as a vapor barrier).

• Typical R-value: R-3.7 per inch (open-cell) to R-6.5 per inch (closed-cell)
• Best uses: Rim joists, attic rooflines (cathedral ceilings), crawlspace walls, around penetrations
• Limitations: Higher cost; professional installation is strongly recommended for most applications; closed-cell can trap moisture if misapplied

Rigid Board Insulation

Rigid foam boards — made from expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (polyiso) — are solid panels cut to fit. They are commonly used on the exterior of foundation walls, under slabs, on exterior wall sheathing, and in low-profile situations where cavity space is limited.

• Typical R-value: R-3.8 to R-6.5 per inch depending on type
• Best uses: Basement walls, under slabs, exterior continuous insulation, roof assemblies
• Limitations: Must be covered with a fire-rated material (drywall or equivalent) when used in living spaces; seams require taping to minimize air leakage

If you're planning an attic conversion, the insulation strategy becomes more complex — our attic conversion planning guide walks through the thermal and structural decisions involved.

Pairing Insulation with Air Sealing

Insulation slows heat transfer, but it does not stop air movement on its own. A drafty home with high R-value insulation will still lose conditioned air through gaps around wiring, plumbing penetrations, and framing joints. Effective thermal upgrades combine insulation with air sealing using caulk, weatherstripping, or foam sealant at penetrations. Our reference on caulk and weatherstripping explains which sealant to use where and how to recognize failure.

Before adding or replacing insulation, check your local building code for the minimum R-value required for your climate zone — requirements vary significantly from southern to northern states. Permits may be required for certain work, particularly spray foam in unventilated assemblies or any project that alters a vapor barrier. Always verify local requirements with your building department before beginning.