Insulation Types Compared: R-Value, Cost & Best Applications

Blown-in cellulose or fiberglass is the best value for attics — $0.50-$1.50/sq ft installed to achieve R-38 to R-60. Cellulose has a slightly higher R-value per inch (R-3.2-3.8) and settles into gaps better. For maximum performance with air sealing, spray foam is superior but costs 3-5x more ($3,000-$7,000 for 1,000 sq ft). For most homeowners, blown-in insulation offers the best return on investment. What R-value do I need?

It depends on your climate zone and where in the house. Attics: R-38 (warm climates) to R-60 (cold climates). Walls: R-13 (2x4 walls) to R-21 (2x6 walls). Floors over crawl spaces: R-25 to R-30. Basement walls: R-10 to R-19. The U.S. Department of Energy has zone-specific recommendations. Higher R-value is always better but has diminishing returns — going from R-19 to R-38 saves more than R-38 to R-60. Is spray foam insulation worth it?

Closed-cell spray foam (R-6-7/inch) is the highest-performing insulation per inch and also creates an air and vapor barrier in one step. It's worth the premium ($1.50-$3.50/sq ft vs $0.30-$1.50 for other types) in specific applications: rim joists, crawl spaces, cathedral ceilings, and when air sealing is critical. For standard attics and walls, blown-in insulation at a fraction of the cost often makes more financial sense. What is the cheapest insulation?

Fiberglass batts are the cheapest at $0.30-$0.80/sq ft for materials (DIY installation). Blown-in fiberglass or cellulose costs $0.50-$1.50/sq ft professionally installed. For attics, blown-in is often cheaper than batts because installation is faster. EPS rigid foam board is the cheapest board insulation at $0.25-$0.50/sq ft per inch of thickness.