Spray foam is sold by the board foot: one square foot, one inch thick. Covering 200 sq ft with 2 in of closed cell foam takes 400 board feet and gives about R-12.4. With 10% allowance that is one Froth-Pak 630 kit, or three Froth-Pak 200 kits.
How the spray foam calculator works
Board feet = area (sq ft) × thickness (in); R-value = thickness × R per inch; kits = board feet × (1 + waste) ÷ kit yield, rounded up
A board foot is a volume: 144 cubic inches, so 12 board feet make one cubic foot. Tiger Foam describes its 600 kit as "529 board feet (square foot at 1″)" and 44 cubic feet, the same arithmetic.
Worked example (the default)
- 200 sq ft × 2 in = 400 board feet
- Closed cell at R-6.2 per inch (Froth-Pak's rating): 2 × 6.2 = R-12.4
- 400 × 1.1 = 440 board feet, ÷ 630 = 0.7, so one Froth-Pak 630; ÷ 200 = 2.2, so three Froth-Pak 200 kits
- Volume: 400 ÷ 12 = 33.3 cubic feet
Open cell vs closed cell
| Open cell | Closed cell | |
|---|---|---|
| R per inch | about 3.6 (DOE); 3.7 for Icynene Classic 45 | 5.5 to 6.5 (DOE); 6.2 for Froth-Pak |
| Density | 0.45 lb/cu ft (Icynene Classic 45) | 2.0 lb/cu ft (Heatlok HFO Pro) |
| R-value of a 2x4 cavity (3½ in) | R-12.6 | R-21.7 |
| DIY kits | Tiger Foam 1350 | Froth-Pak 200 and 630, Tiger Foam 200 and 600, Touch 'n Seal |
Closed cell packs almost twice the R-value into each inch, so an inch or two on a rim joist or a basement wall does what takes a full cavity of open cell. Open cell is lighter and, per Fixr, cheaper per board foot ($0.44 to $0.65 against $1 to $1.50 for the material).
Spray foam kit sizes
Kit names are theoretical yield in board feet. DuPont says it plainly: "Theoretical yield calculations are performed in laboratory conditions, without taking into account the loss of blowing agent or the variations in application methods and types." Expect less than the label; the waste allowance is there for that.
| Kit | Theoretical yield |
|---|---|
| Froth-Pak 200 | about 200 board feet |
| Froth-Pak 630 | about 630 board feet |
| Tiger Foam 200 FR | 180 board feet |
| Tiger Foam 600 FR | 529 board feet |
| Tiger Foam 1350 (open cell) | 1,350 board feet |
Froth-Pak is Class A fire rated up to 2 in thick, according to DuPont. Thicker than that, check the fire rating with your building department before you spray.
How thick to spray
Thickness is a choice of R-value. For the R-values your climate zone calls for, see the insulation calculator. Two inches of closed cell (R-12.4) on a rim joist, or a full 3½ in of open cell (R-12.6) in a 2x4 wall, land at about the same R-value. The drawing under the result shows your thickness against the stud depth (2x4 is 3½ in, 2x6 is 5½ in, per ProWood's actual lumber sizes); foam deeper than the studs has to be trimmed flush before drywall goes on.
How many board feet in a wall?
A 10 ft long, 8 ft tall wall is 80 sq ft. At 3 in of foam that is 240 board feet, 264 with the allowance: one Froth-Pak 630 kit, or two Froth-Pak 200 kits. Subtract windows and doors from the area. The studs take up part of the wall, so counting the full area errs toward a little extra foam.
Next steps
Get an installed price, open or closed cell, from the spray foam insulation cost calculator. For the attic floor, compare loose-fill: count bags with the blown in insulation calculator. Once the foam is trimmed, the drywall calculator counts the sheets to close the wall. More tools are in drywall, paint and walls.