Polyiso vs Eps vs Xps Foam Board Insulation
Expanded Polystyrene and Extruded Polystyrene are cousins but have different DNA when you’re dealing with commercial projects. Both use polystyrene beads, but the manufacturing process creates different density profiles and moisture handling capabilities.
EPS (Expanded Polystyrene) gets made by expanding pre-expanded beads in a mold using steam. The result is lower density around 1.5 to 2.0 lbs/cu ft. You’ll see these as white beadboard insulation that’s cheaper but less water-resistant.
On an interior partition wall, this saw slices through 3-inch EPS with the DeWalt DWE7491RTSliding Compound Miter Saw. The trade-off is EPS absorbs moisture faster and its R-value degrades when it gets wet. But for budget-conscious contractors working on school buildings or municipal projects, it’s unbeatable.
Real product specs:
Owens Corning FOAMULAR 210 EPS Board
– R-Value: R-3.6 to R-4.2 per inch (varies by density)
– Thickness options: 2″, 3″, 4″, 6″, 8″
– Density: 1.7 lbs/cu ft at R-3.6, up to 2.0 lbs/cu ft for higher R-value
– Price range: $0.25 to $0.40 per sq ft
Dow STYROFOAM™ 15 EPS Board
– R-Value: R-3.8 to R-4.2 per inch
– Thickness options: 2″ to 6″
– Price range: $0.30 to $0.45 per sq ft
XPS (Extruded Polystyrene) comes out as a solid sheet, not beads. The extrusion process creates closed-cell structure with density around 2.0 lbs/cu ft minimum. These boards handle moisture way better than EPS and maintain their R-value when exposed to damp conditions.
For slab-on-grade work where contractors need something that won’t wick groundwater up into the foundation, XPS is the standard choice in 2026. The green facer is the giveaway—green means XPS, blue or pink usually means polyiso.
Real product specs:
Dow STYROFOAM™ 450 XPS Board
– R-Value: R-5.0 per inch at 75°F
– Thickness options: 1″, 2″, 3″
– Density: 2.0 lbs/cu ft minimum
– Moisture resistance: Excellent—absorbs less than 2% water by volume
– Price range: $0.60 to $1.00 per sq ft
Owens Corning FOAMULAR™ 300 XPS Board
– R-Value: R-5.0 per inch at 75°F
– Thickness options: 1″, 2″, 3″
– Price range: $0.65 to $0.95 per sq ft
