Closed-cell SPF: 2 lb/cf density. R-value: 6.5/inch (highest of any common insulation). Also functions as: air barrier, vapor retarder (Class II at 1.5in), structural racking when applied to wall sheathing. Blowing agent: HFO (low-GWP). Application: professional only, 2-component spray. Maximum lift: 2 inches per pass. Cure time: tack-free 30-60 sec, full cure 24 hrs. Must pass fire testing (NFPA 286) or be covered with 15-min thermal barrier (1/2in gypsum). Cost: $1.50-$3.00/board foot installed. Disadvantages: expensive, professional-only, off-gassing concerns during install (24-hr vacate recommended), difficult to remove/modify. CSI 07 21 16.