The innovative fiberglass reinforced thermoset polymer (FRT) structural ‘skin’ is the most advanced engineered material available for structural wall panel applications. CPBS has combined the best, proven polyurethane foam core technologies with FRT skins to create the revolutionary Composite Structural Insulated Panel (C-SIP) and Composite Structural Insulated Sheathing (C-SIS) building products. The wall panel’s interior and exterior skins create far superior strength and energy efficiency, while eliminating thermal transfer and dramatically reducing any air, water or vapor infiltration.  The same type of FRT materials are used extensively in the marine and aircraft industries for their durability, high performance and long term sustainability. The following is a list of the unique FRT skin’s performance advantages:

  1. The FRT skins are made using a thermoset resin composite system, which forms them into a permanent shape when they are cured (set) by heat, creating a long term sustainable material that will not lose its structural performance or fundamental properties over time.
  2. High ambient temperatures will not melt, warp or re-shape the FRT skins like they can with inexpensive thermoplastics skins.
  3. During manufacturing, the FRT skins are bonded to the polyurethane foam by a chemical reaction after the foam injection into the panel mold – not assembled with glue.  Conventional SIP panels and sheathings are made with slabs of EPS or XPS foam cores that are glued to the OSB skins during assembly; this method counts on the strength of the glue to keep them together – making them susceptible to coming apart, delaminating, if the glue fails from improper quality control during manufacturing or continued exposure to hot and cold or wetting and drying cycles.
  4. The cross linked polymers in the FRT skins yield a stronger and more stable structural skin that is impervious to water – unlike wood-based or fibrous materials that are prone to moisture and mold problems.
  5. The FRT composite skin and joint sealing system work together to block air and water infiltration. No house wrap is needed.
  6. Nails cannot penetrate the FRT skin, only self-tapping screws can be used due to the skin’s durable polymer composition. Screws will not work themselves loose and pop out of the wall surface unlike construction nails vulnerable to movement from wood shrinkage.
  7. The FRT skin was expressly designed as a vapor retarder for extreme climates such as the Gulf Coast of the U.S. where hot and humid conditions (Climate Zones 1 & 2) can drive moisture directly through exterior finishes.
  8. C-SIP and C-SIS have been manufactured and tested to be installed and left unfinished for up to 180 days.

Thermoset vs. Thermoplastic

Though thermoset and thermoplastics sound similar in name, they have very different properties and applications. Understanding the performance differences can help you make better decisions in selecting your building materials.


A thermoset is a polymer that hardens or sets through a curing process. Curing is an irreversible chemical reaction in which permanent connections, known as cross-links, are made between the material’s molecular chains. These cross-links give the cured polymer three-dimensional structure, as well as a higher degree of rigidity than it possessed prior to curing. A thermoset cannot be reheated and re-shaped after it is cured. Thermoset polymers outperform thermoplastics in a number of areas, including mechanical properties, chemical resistance, thermal stability, structural integrity and overall durability.


A thermoplastic is a polymer that becomes pliable with heat and returns to a solid state upon cooling. Changes seen in molded thermoplastics are purely physical. That is, with the reapplication of heat, the physical change is wholly reversible as no chemical bonding, or cross-linking, takes place. Therefore, a thermoplastic material can be reheated and reshaped. In this way, thermoplastics differ from thermoset polymers, which form irreversible chemical bonds during the curing process.