Polyurethane vs. Polystyrene SIPs
Polyurethane Foam
- Closed Cell Foam
- Non-Permeable
- Perm rate of 1 or less
- R- Value 7-7.5 per inch
- Complete vapor barrier
- Chemical process bonds foam to “skin” no supplemental adhesive required
- Resistant to mold and mildew
- Class A fire rating
- Chemical resistant foam
- Pre-installed foam tongues and headers
- Less field labor
- Less field waste
- Thermally broken structural members
- Complete thermal barrier
- No off gassing
Polystyrene (EPS/XPS) Foam
- Closed Cell Foam
- Permeable Foam
- Perm rate of 3 or higher
- R- Value 3.5- 4 per inch
- Requires supplemental vapor barrier
- Secondary mechanically applied adhesive
- Susceptible to mold and mildew
- Foam melts at 300°F
- Foam degrades when exposed to petroleum based adhesives and solvents
- On-site install of splines and headers
- Increased field labor
- Increased field waste
- Structural members create thermal bridging
- Thermal bridging
- Contains benzine, a know carcinogen
The characteristics of polyurethane foam structural insulated panels have several advantages over the polystyrene foam panels. The most obvious advantage comes in the R-values of the different foams. Because polyurethane foam has a higher R-value per inch it is possible to increase the living space of a building versus the living space of a Polystyrene SIP building with the same footprint. This also allows more flexibility for the architect dealing with details throughout a design.
Specifically, with Earthcore SIPs, it is possible to have a completely thermal bridge free wall assembly. Earthcore uses rSTUD™ for all structural members contained within the panel. These products are thermally broken studs and headers and are exclusive to Earthcore SIPs.
One of the most important differences between polyurethane and polystyrene SIPs is the permeability of the foams. While both foams are considered closed cell, only polyurethane foam is considered a complete vapor barrier. The reason for this is that the perm rate of polyurethane foam is 1 or less while polystyrene is 3 or more. Over time the absorption of moisture in a polystyrene panel can cause de-lamination as well as the growth of mold and mildew. Tests also show that moisture can inhibit the thermal performance of the panels reducing effective R-value.
Finally, polystyrene panels use a flame retardant in order to reduce their flammability. The particular flame retardant that they use contains benzine which is a known carcinogen. The European Union is concerned enough that they have moved to outlaw the use of any products containing benzine.