Using Graphite Polystyrene (GPS) Insulation
A new acronym coming your way.
Perhaps you’re thinking, “But, I already know what that is—the nifty device that keeps me from getting lost on the drive to a new job site.” True enough, but it is also the name of a new class of rigid foam insulation for wall applications—graphite polystyrene (GPS).
Available throughout the U.S. under various brand names, GPS integrates high-purity graphite into an expanded polystyrene (EPS) polymer matrix to enhance the insulation’s R-value. The result is a lightweight, thin product that is easily identified by its gray/platinum color.
GPS Insulation Attributes
With dozens of insulation options to choose from, you might be wondering about the need for yet another one. Following is an overview of the performance attributes and applications of GPS, and how it compares to other rigid foam insulations.
The graphite in GPS insulation enhances the material’s R-value as temperatures decrease. Compared to other polystyrene-based and polyiso rigid foams, GPS retains more of its R-value in colder temperatures. And, like its sister material EPS, manufacturers produce GPS with blowing agents that do not diffuse during the insulation’s time in service, so the insulation does not experience thermal loss as some rigid foams do.
Depending on the insulation thickness and density, GPS has a permeability rating ranging from 2.5 to 5.5, which allows for movement of water vapor out of the wall assembly. The insulation also shares EPS insulation’s trait of drying quickly and having minimal long-term moisture retention. These two attributes make GPS insulation well-suited for high-moisture environments.
A key benefit that GPS insulation offers is the ability to achieve higher R-values with thinner sheets of material, which helps ensure thermal performance even in space-constrained wall assemblies.
Manufacturers offer GPS insulation in numerous product configurations suited to both residential and commercial wall applications. This includes both faced and un-faced insulation sheets. Applications include:
- Wall sheathing systems
- Continuous insulation
- Exterior insulation and finishing systems (EIFS) and stucco systems
- Pre-cast or tilt-up walls
- Structural insulated panels
As a high-performance insulation, GPS is priced somewhat higher than standard EPS insulation, but offers 20 to 30 percent lower material cost over other premium rigid foam insulations. The lightweight insulation also lowers shipping costs and speeds installation times, considering it obviates the need to build up layers of individual sheets. For building owners, such high performance insulations also provide energy cost savings year-after-year.
Is any single insulation ideal in all wall applications? Of course not! But GPS offers another choice to consider, especially in assemblies where limited thickness of the insulation is crucial, such as in cold-climate residential construction where homeowners don’t want fortress-like walls.