Insulation R-value per inch
Every material adds a different R-value per inch, so the thickness you need for R-49 varies a lot. Pick a material for its thickness chart, or compare them all in the calculator.
Blown-in fiberglass
R-2.5 / inch
Attics (most common attic material)
Blown-in cellulose
R-3.5 / inch
Attics and dense-packed walls
Fiberglass batt
R-3.1 / inch
Walls, floors, and accessible joist bays
Mineral wool (rock wool) batt
R-3.3 / inch
Walls needing fire and sound resistance
Open-cell spray foam
R-3.6 / inch
Walls and ceilings; also air-seals
Closed-cell spray foam
R-6.5 / inch
Tight spaces, rim joists, crawlspaces (highest R per inch)
EPS rigid foam board
R-3.8 / inch
Continuous exterior sheathing (budget)
XPS rigid foam board
R-5 / inch
Foundation and below-grade walls
Polyiso rigid foam board
R-6 / inch
Continuous sheathing (highest-R board)