How to Choose Your Core

Beginning in the 3rd quarter of 2012, Foard Panel expaned from two to four different foam core materials. Our original core foams, EPS and XPS, will continue with no changes. We added polyiso (PIR) & Neopor (NEO) cores.
This bulletin provides guidance to help specify the core best suited to your project.
Structural and thermal examples are listed to help illustrate the differences between cores under differing conditions. To ease comparison to other technical information, this document complies with federal regulations1 and SIPA guidelines2. Consult the Foard Panel Data Sheet for the panel of interest to find more details.


Pro: Structural properties – EPS is the most mature, most heavily tested, and best documented of all core materials. Only EPS-core SIPs have IBC/IRC-level code listings in the US.
Pro: Very high R-Value per dollar ratio.
Pro: Easiest core to work – Edge rout with panel routers, hot wires, & foam-scoops.
Con: Moderate R-value per inch, about the same as most conventional infill insulation.


Pro: Structural properties – XPS has the highest shear, tensile, and compressive strength of all cores.
Pro: High R-Value per inch ratio.
Pro: Easy to work – Edge rout with panel routers, hot wires, & foam-scoops.
Pro: Available in 6 specific thicknesses.
Con: Lowest R-value per dollar ratio.

Polyiso3 (Urethane3)

Pro: Highest R-Value per inch ratio.
Pro: Very high R-value per dollar ratio.
Con: Structural properties – Polyiso and Urethane have the lowest structural properties of all available core materials, based on all available test data. For this reason, Foard Panel doesn’t recommended polyiso or urethane SIPs transverse load conditions.


Pro: Structural properties – Similar properties to EPS. Foard is qualifying Neopor for the exising EPS code listing.
Pro: Higher R-value per inch than EPS.
Pro: Just as easy to work as EPS – Edge rout with panel routers, hot wires, & foam-scoops.

Core Type EPS XPS Polyiso (PIR) Neopo (NEO)
Max roof span for 8.25” SIP 80 lb/sqft load @ L/240 11 ft 14 ft 4 ft 11 ft
Max pressure for 4.5” SIP wall 8' vertical span L/240 52lb/ft2 75lb/ft2 30lb/ft2 52lb/ft2
6.5” SIP whole-surface R-value R-23 R-30 R-35 R-26
SIP Thickness required to meet R-494 ceiling spec. in IECC code 10.25" 8.25" 6.5" 8.25"
Available SIP Thicknesses Any Thickness 3"-25" 3.0 4.5 6.5 8.25 10.25 112.25 3.0 4.5 6.5 8.25 10.25 12.25 Any Thickness 3'-25"
R-Value Range Min. R-10 R-12 R-14 R-11
R-Value Range Max. R-93 R-58 R-70 R-110

Contact & Technical Support

If you have any questions about any of these items, please feel free to contact me or any one of the Foard Panel project managers.
Paul Malko
Technical Director
Selecting SIP cores pdf

1 US Code of Federal Regulations Title 16, Part 460
2 Structural Insulated Panel Association, Published R-Value Guidelines,
3 Polyiso is a nickname for polyisocyanurate foam and urethane is a nickname for polyurethane foam. Polyiso and urethane foam of the same density have basically the same thermal and structural properties, according to chemistry suppliers that serve the SIP industry. For more information see Foard Panel Technical Bulletin “Why Polyiso/Urethane SIPs are Non-Structural”.
4 The IECC-2009 assumes light wood frame & infill style construction and allows other building systems with equivalent performance of a light wood frame & infill assembly with the stated R-value of insulation in the cavity. The reason SIPs can use much lower R-values and still meet this requirement is because the IECC assumes that a large portion of it’s surface area as thermal bridges where SIPs do not. See Foard Panel Technical Bulletin “SIPs and the IECC”