Best Rigid Foam Insulation for DIYers
Rigid foam board insulates walls, basements, foundations, and roofs with high R-value per inch and moisture resistance that fiberglass cannot match. The three types, XPS, EPS, and polyiso, trade off R-value, cost, and moisture handling.
What to look for
- ·XPS (pink/blue) is strong and moisture-resistant for basements and foundations; EPS (white) is cheapest; polyiso (foil-faced) has the highest R-value for walls and roofs.
- ·Use rigid foam for continuous exterior insulation, basement walls, under slabs, and to boost R-value where space is tight.
- ·Seal seams with the right tape and foam, and check fire code, foam usually needs a thermal barrier (like drywall) when used inside.
Quick comparison
| Product | Tier | Price | Best for |
|---|---|---|---|
| Owens Corning Foamular XPS | Editor's pick | $20 to $45 per sheet | Basements and moisture areas |
| Kingspan Polyiso (Foil-Faced) | Editor's pick | $25 to $50 per sheet | Maximum R-value walls/roofs |
| DuPont Styrofoam XPS | Editor's pick | $20 to $45 per sheet | Durable moisture resistance |
| Foam Board XPS (Home Center) | Best value | $15 to $35 per sheet | Value XPS |
| R-Tech EPS Foam Board | Best value | $12 to $28 per sheet | Value continuous insulation |
| Foamular 150 XPS | Best value | $15 to $35 per sheet | Value general XPS |
| EPS Foam Board (Store) | Budget pick | $8 to $20 per sheet | Budget general insulation |
| Thin Foam Sheathing | Budget pick | $10 to $22 per sheet | Budget thermal break |
| Basic Foam Board | Budget pick | $6 to $16 per sheet | Lowest-cost small jobs |
Editor's pick
Owens Corning Foamular XPS
$20 to $45 per sheet
The well-known pink XPS board, strong and moisture-resistant with about R-5 per inch, ideal for basements, foundations, and continuous insulation. The trusted pick.
Best for: Basements and moisture areas
Typically available at Home Depot, Lowe's.
Kingspan Polyiso (Foil-Faced)
$25 to $50 per sheet
A high-R-value foil-faced polyiso board (about R-6+ per inch) for walls and roofs where you want the most insulation per inch. The pick for maximum R-value.
Best for: Maximum R-value walls/roofs
Typically available at Home Depot, Insulation suppliers.
DuPont Styrofoam XPS
$20 to $45 per sheet
The classic blue XPS board with strong moisture resistance and durability for foundations and continuous insulation. A premium, proven pick.
Best for: Durable moisture resistance
Typically available at Home Depot, Lowe's.
Best value
Foam Board XPS (Home Center)
$15 to $35 per sheet
Home-center XPS foam board at a value price for basements, walls, and general insulation. A strong value with good moisture resistance.
Best for: Value XPS
Typically available at Home Depot, Lowe's.
R-Tech EPS Foam Board
$12 to $28 per sheet
An EPS foam board with a laminated facer at a good value, used under siding and slabs and for general insulation. A solid value for continuous insulation.
Best for: Value continuous insulation
Typically available at Home Depot, Lowe's.
Foamular 150 XPS
$15 to $35 per sheet
A standard-density XPS board for walls and general insulation at a value price. A dependable mid-value pick with good moisture resistance.
Best for: Value general XPS
Typically available at Home Depot, Lowe's.
Budget pick
EPS Foam Board (Store)
$8 to $20 per sheet
Basic white EPS foam board at the lowest cost for general insulation and crafts. Lower R-value per inch than XPS, but the cheapest rigid foam.
Best for: Budget general insulation
Typically available at Home Depot, Lowe's.
Thin Foam Sheathing
$10 to $22 per sheet
Thin foil or laminated foam sheathing for a continuous insulating layer under siding at a low cost. Modest R-value, but a budget way to add a thermal break.
Best for: Budget thermal break
Typically available at Home Depot, Lowe's.
Basic Foam Board
$6 to $16 per sheet
The cheapest rigid foam board for small insulating jobs, crafts, and filling gaps. Basic and lower-R, but a low-cost option for non-critical use.
Best for: Lowest-cost small jobs
Typically available at Home Depot, Lowe's, Amazon.
Frequently asked
What is rigid foam insulation used for?+
Continuous insulation on exterior walls (under siding), insulating basement and foundation walls, under concrete slabs, on roofs, and anywhere you need high R-value in a thin, moisture-resistant board. Its rigidity and moisture resistance make it ideal where fiberglass batts would absorb water or not fit.
XPS, EPS, or polyiso, which foam board?+
XPS (extruded, pink or blue) is strong and moisture-resistant, great for basements, foundations, and under slabs. EPS (expanded, white) is the cheapest with good value and is used widely under siding and slabs. Polyiso (foil-faced) has the highest R-value per inch, best for walls and roofs above grade (but loses some R-value when very cold).
What R-value does foam board have?+
Per inch, roughly: EPS about R-3.6 to R-4, XPS about R-5, and polyiso about R-6 to R-6.5. So a thinner foam board can match thicker fiberglass. Add up the inches for your target R-value, and remember foam often supplements other insulation as a continuous layer.
Can I leave rigid foam exposed?+
Usually no inside living spaces, most foam is combustible and building codes require a thermal barrier (commonly 1/2-inch drywall) over it for fire safety. In some unfinished areas an intumescent coating or specific fire-rated board is allowed. Always check local code before leaving foam exposed indoors.
How do I install rigid foam board?+
Cut it with a utility knife (score and snap) or saw, fit it tightly between or over framing, fasten with foam-board adhesive or cap nails/screws, and seal the seams and edges with the proper foam tape or spray foam to stop air leaks. For exterior continuous insulation, integrate it with the water-resistive barrier per the maker.