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

Why Insulation Type Matters

Choosing the right insulation isn't just about stuffing material into a wall cavity — it's about matching the product's physical properties to your specific application, climate zone, and budget. Each insulation type behaves differently when it comes to air sealing, moisture resistance, and ease of installation. Getting this wrong can lead to thermal bridging, condensation problems, or simply underperforming walls that drive up energy bills.

The three most common residential insulation types — batt, spray foam, and blown-in — each have a distinct set of strengths. Use this guide as a quick-reference lookup to understand what each offers and where it makes the most sense. For a broader approach to reducing energy loss throughout your home, see our room-by-room weatherproofing guide.

Batt Insulation

Batt insulation — typically fiberglass or mineral wool — comes in pre-cut panels sized to fit standard stud and joist spacing. It's one of the most cost-accessible DIY-friendly options and is widely available at home improvement stores.

• R-value range: Approximately R-3.0 to R-4.3 per inch for fiberglass; R-3.7 to R-4.2 per inch for mineral wool
• Best applications: Open wall cavities, attic floors between joists, and floor assemblies with standard framing
• Key limitations: Batts must be cut and fitted carefully around obstructions; gaps or compression significantly reduce effective R-value. They provide little air-sealing benefit on their own.

Installation note: Proper fit is critical. Batts that are jammed, folded, or compressed lose thermal performance. Always wear gloves, eye protection, and a dust mask when handling fiberglass batts.

Spray Foam Insulation

Spray polyurethane foam (SPF) expands on contact to fill irregular gaps and cavities, making it uniquely effective as both an insulator and an air barrier. It comes in two main formulations: open-cell and closed-cell.

• Open-cell foam: Softer, less dense, approximately R-3.5 per inch. Vapor-permeable, so it's often used in climate zones where some moisture movement is acceptable.
• Closed-cell foam: Dense, rigid, approximately R-6.0 to R-7.0 per inch. Acts as a vapor retarder and provides structural rigidity. Better suited for crawl spaces, rim joists, and exterior-facing applications.
• Best applications: Rim joists, cathedral ceilings, crawl spaces, and anywhere air infiltration is a primary concern

Important: Full spray foam application is generally not a DIY task. Professional installers use specialized equipment and must follow safety protocols during application. Small canned foam (for gaps and cracks) is different from full-cavity spray foam systems. Permits or inspections may be required in some jurisdictions — verify with your local building department.

Blown-In (Loose-Fill) Insulation

Blown-in insulation — made from cellulose, fiberglass, or mineral wool — is machine-blown into place, making it ideal for irregular spaces and hard-to-reach areas. It conforms around existing framing, wiring, and ducts better than batts.

• R-value range: Approximately R-2.2 to R-3.8 per inch depending on material and settling
• Best applications: Existing attics, enclosed wall cavities (requires drilling access holes), and spaces with many obstructions
• Key advantages: Cellulose is made largely from recycled content; blown-in generally covers obstructions more uniformly than batts
• Key limitations: Cellulose can settle over time, reducing effective depth; moisture management is critical

Many home improvement retailers offer blower machine rentals when you purchase a sufficient quantity of material, making this a viable DIY project for attic top-ups. Enclosed wall applications typically require a contractor with the appropriate equipment and expertise.