Insulation is a critical component to specify when designing a functional, cost-effective, and energy-efficient building. One method to insulate a building is by installing 50 to 152 mm (2 to 6 in.) of rigid foam insulation on the exterior side of the wall framing. Two of the most frequently installed types of rigid foam insulation are expanded and extruded polystyrene (EPS and XPS). Both serve the same basic function: providing a means to manage the passage of heat in a building system. However, they differ in important ways.
The primary responsibility of any insulating construction material is to offer positive thermal performance. However, this is not the only factor to account when specifying a rigid foam insulation material. It is also critical to know how it will perform under several situations.
XPS is manufactured in a continuous extrusion process that produces a closed cell form of foam insulation. EPS, on the other hand, is manufactured by expanding spherical beads in a mold and then using heat and pressure to fuse the beads together.
Each product has proponents claiming one out performs the other. However, it is key to understand each product may be more suited for a particular use than the other. This can be made clearer by examining each product’s thermal and moisture protection, fire and water resistance, and implications for sustainably designed projects.