Comparisons
Rigid Foam vs Spray Foam
Both are foam plastic insulation with high R per inch. One comes in sheets you cut, the other arrives as a liquid that expands in place. The choice usually comes down to geometry and budget.
Updated January 2026 · about 7 min read
R-value per inch
EPS: R-3.6 to R-4.2. XPS: R-5 (drifts toward R-4.5 with age). Polyiso: R-5.6 to R-6.5, but loses performance in very cold temperatures. Closed-cell spray foam: R-6 to R-7 and stable.
Cost
Rigid board is $0.45–$1.30 per sq ft per inch as material, and a competent DIYer can install it. Closed-cell spray runs $1.00–$1.75 per board foot installed. For big flat surfaces, board is far cheaper.
Gear for this job
Multi Purpose XPS Foam Board,2 Pack 15.6x11.7X 2in Polystyrene Craft Foam Sheets,Rigid and Easy to Shape,DIY Modeling Art Projects, Party Decoration, Cosplay Prop Production, Carve,Heat Insulation
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LuckyFoam Blue 4 Pack 15x12x2 inch Foam Sheets 2 Inch Thick | Polystyrene Rectangles XPS Foam Board Craft for Insulating DIY Modeling Art Supplies
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Fabbay 2 Pcs Pink XPS Foam Board 15" X 12" 2" Thick Rectangle Craft | Polystyrene Foam for Insulation, Modeling Art Supplies, Lightweight Pink Boards, Easy to Cut and Shape for DIY Projects
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F&L R6 Fiberglass Board Acoustic Insulation Panels – 1" to 2" Thick, 24"x24" and 24"x48" – Thermal Soundproofing for Walls, Ceilings, Studios & HVAC Duct Applications (1-1/2in x 24in x 48in)
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Air sealing
Spray foam seals itself. Board only seals if you tape every seam and foam every edge — do that and taped board is an excellent air barrier, skip it and it is nearly useless as one.
Where each wins
Board: basement walls, exterior continuous insulation, slab edges, garage doors, flat roofs, anywhere you can cut a rectangle. Spray: rim joists, irregular bays, cathedral ceilings, crawl spaces, and retrofits full of pipes and wires.
Run the numbers
Frequently asked questions
- Which foam board is best for basement walls?
- XPS or foil-faced polyiso, taped at the seams. EPS also works and is more vapor open, which some builders prefer below grade.
- Does foam board need to be covered?
- Yes. Interior foam requires a code-approved thermal barrier — usually 1/2 inch drywall — for fire safety.
- Can I combine them?
- Commonly, yes: rigid board on flat areas and canned or two-part foam to seal the edges and awkward corners.
Insulation gear worth owning
The tools and materials that show up on almost every insulation job.
Multi Purpose XPS Foam Board,2 Pack 15.6x11.7X 2in Polystyrene Craft Foam Sheets,Rigid and Easy to Shape,DIY Modeling Art Projects, Party Decoration, Cosplay Prop Production, Carve,Heat Insulation
Check price on Amazon
Multi Purpose XPS Foam Board,2 Pack 15.6x11.7X 2in Polystyrene Craft Foam Sheets,Rigid and Easy to Shape,DIY Modeling Art Projects, Party Decoration, Cosplay Prop Production, Carve,Heat Insulation
Check price on Amazon
BEEST FullStop Spray Foam Insulation Kit - 240 Board ft/sq.ft. Fire Rated Spray Insulation Foam for Walls & Attics with Thermal & Soundproofing - Includes 12x Cans, 1 Cleaner, Pro X Gun, Safety Gear
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XFasten Foam Pipe Insulation Tape 2 Inch x 15 Feet Heavy-Duty AC Line Insulation Outdoor Pipe Wrap Tape AC Pipe Insulation Outdoor Pipe Insulation Wrap Tape HVAC Line Insulation Pipe Wrap Around Tape
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As an Amazon Associate we earn from qualifying purchases. Product links on this page may earn us a commission at no extra cost to you.