Rigid-foam insulation packs a lot of R-value into a thin package, but not all rigid foam performs the same. Choose rigid insulation wisely, and consider the effect its characteristics will have on the performance of the your project, overall product cost, and the best way to get the bang for your buck.
Expanded polystyrene (EPS)
The most versatile of the three rigid insulation options, EPS is used in Roof, Wall, Floor, Below Grade & Structural GeoFoam applications. EPS foam is the insulation used most widely in insulated concrete forms and structural insulated panels. With the highest average R-value per dollar of the three types of rigid-foam insulation (about 4.6 R per inch), EPS foam costs the least, while meeting or exceeding all required building and energy codes. EPS is approved for ground contact, below grade applications and can be treated to resist insects, and it does not retain water over the long term. When applied as sheathing, EPS should be used over house wrap, or with a product that incorporates a factory laminated option. EPS is available faced or unfaced. Faced products are considered vapor retardant and specialty products are considered vapor barriers. EPS manufacturers (such as Insulfoam) typically warrant 100% of EPS’ R-value over the long term as EPS foam R-value does not degrade over time.
Extruded polystyrene (XPS)
Easily recognized by its blue, green, or pink color, extruded polystyrene falls in the middle of the three types of rigid-foam insulation in both cost and R-value. Used most in walls or below grade applications, XPS is recyclable, and at about R-5 per inch, costs around 42¢ per sq. ft. for a 1-in.-thick 4×8 panel. XPS comes unfaced or with a number of different plastic facings. Unfaced 1-in.-thick XPS has a perm rating around 1, making it semipermeable. Thicker and faced XPS is stronger and can have a lower perm rating, but either way, it is considered a vapor retarder, not a vapor barrier. XPS absorbs more moisture than other insulations over the long term, and as a result its warranty doesn’t honor R-value retention over the long haul.
Polyisocyanurate (Polyiso, ISO)
Most used in roofing applications, ISO panels are expensive, costing as much as 70¢ per sq. ft. for a 1-in.-thick panel, and they pay off with (aged) R-values as high as R-6.5 per inch. (R-values start around R-8 and degrade slightly over time.) The manufacturing process for ISO is one that is not environmentally friendly, and starts with liquid foam, further ISO is not able to be recycled. Because ISO starts as liquid foam and has to be sprayed against a substrate to form a rigid panel, all ISO panels are faced. A few different facings used on ISO affect the performance of the panel in both durability and perm rating. Foil-faced ISO panels are considered impermeable. Because applying these products as sheathing creates an exterior vapor barrier, they never should be used with an interior vapor barrier. More permeable ISO panels are faced with fiberglass and can be used without creating a vapor barrier.
Insulfoam EPS Rigid Foam Insulation
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