2 inch foam board insulation is the workhorse panel for basement walls, exterior sheathing under siding, slab edge insulation, and continuous insulation over wood studs. It hits R-10 in XPS and R-12 in polyiso, fits cleanly between 2x6 studs as an exterior layer, and cuts to size with a utility knife. After comparing current 2 inch panels from the four major manufacturers, these five products stood out for compressive strength, moisture absorption, R-value retention, and price per square foot.
Quick comparison
| Panel | Foam type | R-value (2 in) | Compressive (psi) | Best for |
|---|---|---|---|---|
| Owens Corning FOAMULAR 250 | XPS | R-10 | 25 | Basement walls |
| DuPont Styrofoam Brand SM | XPS | R-10 | 15 | Above grade walls |
| Kingspan GreenGuard EPS | EPS | R-8 | 15 | Slab edge |
| Atlas EnergyShield Pro | Polyiso | R-13 (warm) / R-10 (cold) | 25 | Exterior sheathing |
| Insulfoam R-Tech EPS | EPS faced | R-8.4 | 15 | Budget basement |
Owens Corning FOAMULAR 250, Best Overall
FOAMULAR 250 is the pink XPS panel that has been the basement insulation default for two decades, and the current version holds the position. 25 psi compressive strength means you can install it under concrete slabs or against backfilled foundation walls without crushing. Water absorption sits below 0.3 percent by volume after 28 day immersion, which is the lowest in the lineup.
The shiplap edges seal cleanly to adjacent panels and the panel cuts straight with a utility knife. R-10 at 2 inches holds steady from 0 F to 100 F, no thermal drift the way polyiso has.
Trade-off: price runs about 35 to 45 dollars per 4 by 8 sheet, the highest in the lineup. For a 1000 square foot basement that is 100 dollars more than the EPS picks, which is worth it for the moisture resistance.
DuPont Styrofoam Brand SM, Best Above Grade
DuPont’s Styrofoam Brand SM is XPS like FOAMULAR but at 15 psi compressive strength instead of 25, which makes it lighter, slightly cheaper, and just as effective for above-grade applications where it is not getting backfilled or driven on. Wall sheathing under siding, attic kneewall insulation, and rim joist sealing all work with the SM grade.
R-10 at 2 inches, water absorption under 0.3 percent, and the same square-edge or shiplap options as FOAMULAR. Available in most home centers, which matters for a job where you need 30 sheets on Tuesday.
Trade-off: not rated for below-slab or backfill use. If you are insulating under a basement floor or behind a foundation wall, step up to FOAMULAR 250 or equivalent 25 psi grade.
Kingspan GreenGuard EPS, Best for Slab Edge
EPS is the right pick for slab edge insulation around a heated slab or a basement perimeter where the panel sits in soil but never gets buried under concrete. Kingspan’s GreenGuard EPS at 2 inches gives you R-8 with an HFO-free blowing agent (lower global warming impact than older XPS formulations).
Density is 1.5 pcf which holds shape under backfill pressure without compressing. The panel ships with a reflective facing on one side that adds a small reflective R bump when installed against a foil-friendly air gap.
Trade-off: EPS absorbs more water than XPS (2 to 4 percent by volume long term in wet soil). For continuously wet sites or below high water table, stay with XPS. For slab edge above good drainage, EPS performs fine and costs roughly 25 percent less.
Atlas EnergyShield Pro, Best Exterior Sheathing
For exterior continuous insulation under siding, polyiso has the highest R per inch (R-6 to R-6.5) and the foil facing reflects radiant heat into the cavity below. Atlas EnergyShield Pro at 2 inches delivers R-13 in warm conditions, dropping to about R-10 in cold weather as polyiso always does.
Foil facing seals tightly with foil tape at every seam, the panel resists wind-driven rain when properly lapped, and the 25 psi compressive strength holds fasteners well during siding install. The panel meets the 2024 IECC continuous insulation requirement in climate zones 4 through 6 at 2 inches.
Trade-off: thermal drift means the R-value drops in winter when you need it most. For a cold climate where exterior temperatures sit below 20 F for months, calculate with R-10, not R-13. Polyiso is also more expensive than EPS by about 40 percent per board foot.
Insulfoam R-Tech EPS, Best Budget
R-Tech is faced EPS with a metalized polymer film on each side that adds physical durability and a small radiant R bump. At 2 inches the panel hits R-8.4, which is below XPS but at roughly half the price per square foot.
For a budget basement insulation job, a garage wall, or a workshop where R-10 vs R-8.4 makes a small monthly heating difference, R-Tech is the practical pick. The metalized facing also doubles as a vapor retarder when seams are taped with foil tape.
Trade-off: EPS is more permeable than XPS, so a wet basement wall can drive moisture into the panel over time. Pair it with good basement waterproofing on the exterior of the foundation, or stay with XPS if you have known seepage issues.
How to choose
Match foam type to moisture exposure
Below grade and below slab demand XPS at 25 psi. Above grade exterior wants XPS, EPS, or polyiso depending on budget and climate. Anywhere wet, skip EPS unless the site is well-drained. Polyiso lives outside, never below grade.
Compressive strength tied to the load
Under a concrete slab you walk on, 25 psi is the minimum. Backfilled against a foundation wall, 25 psi works for residential depths. Light commercial or driven-over surfaces need 40 psi or higher. For most homeowner projects, 25 psi covers everything except under-slab use where heavy equipment may sit.
Tape every seam
Untaped seams let air leak through the assembly and cut the effective R-value of the wall by 15 to 30 percent. Use foil tape on foil-faced polyiso and EPS, use the manufacturer-specified tape on XPS, and seal corners with closed-cell spray foam in a can. The taping step is the cheapest performance upgrade on any foam board install.
Thermal barrier inside, weather barrier outside
Code requires 1/2 inch drywall (or equivalent thermal barrier) over foam inside conditioned space. Outside, foam needs a drainable rainscreen or a tight WRB tape job to keep wind-driven rain from getting behind the panel.
For related building work, see our guide on attic insulation types r-value and the breakdown in basement waterproofing methods. For details on how we evaluate building materials, see our methodology.
2 inch foam board insulation is the right thickness for most residential applications: deep enough to hit R-10 in XPS, thin enough to install without changing wall framing or window trim. FOAMULAR 250 is the right pick for any below-grade or moisture-prone work, EnergyShield Pro is the answer for exterior sheathing in moderate climates, and R-Tech EPS is the budget option for dry above-grade applications. Spec the panel to the moisture risk first, the R-value second, and the install holds for the life of the building.
Frequently asked questions
What R-value does 2 inch foam board give me?+
It depends on the foam type. 2 inch polyiso runs R-12 to R-13 at room temperature but drops to R-9 to R-10 in cold weather because of the thermal drift effect. 2 inch XPS sits at a steady R-10. 2 inch EPS lands at R-8 to R-8.4. For most 2026 code calculations on basement walls and exterior sheathing, expect to count 2 inch foam board as R-10 unless you are using polyiso in a warm climate.
Can foam board be installed directly against a concrete basement wall?+
Yes, and this is the recommended assembly in most cold-climate building codes. The foam acts as both insulation and a vapor retarder, which stops warm interior air from condensing on the cold concrete face. Use foam-rated adhesive (PL 300 or Loctite PL Premium Max), tape every seam with foil tape, and seal the bottom edge with a closed-cell sill sealer. No interior poly vapor barrier behind drywall; that creates a double vapor barrier and traps moisture.
Do I need a thermal barrier over foam board indoors?+
Yes. Most foam boards are combustible and emit toxic smoke when they burn, so building codes require a thermal barrier (typically 1/2 inch drywall) between the foam and the conditioned space. The exception is some thermal-barrier-rated faced products that allow direct exposure in unfinished areas, but the rules vary by jurisdiction. For any finished basement or living space, assume drywall over foam is required.
XPS vs EPS vs polyiso for below-grade walls?+
XPS is the default for below-grade work because it absorbs the least water (under 0.3 percent by volume) and holds its R-value when buried in damp soil. EPS is cheaper and more vapor-permeable, which can help walls dry but lets in more moisture in wet sites. Polyiso loses R-value in cold and absorbs more water than XPS, so it is rarely the right pick for below-grade. Use XPS for foundation walls and basement rim joist insulation.
Can I cut 2 inch foam board with a utility knife?+
Yes, all three foam types cut cleanly with a sharp utility knife or a long-blade insulation knife. Score one side, snap the panel, and finish through the back with the knife. For long straight cuts use a straightedge guide. For curves and outlet cutouts, use a hot wire foam cutter or a fine-tooth handsaw. A circular saw works but throws static-charged dust that sticks to everything in the work area.
