COST: Varies widely, but filling a 2--4 cavity to R-13 with closedcell spray foam costs about $1.75 to $3 per sq. ft. Closed-cell spray foams provide a higher R-value per inch than less expensive insulation types like fiberglass, cellulose, or open-cell foam, all of which have R-values of R-3.2 to R-3.8 per in.Jan 24, 2012read more >>