XPS foam is a rigid, closed-cell foam insulation made from extruded polystyrene resin. Unlike its cousin, Expanded Polystyrene (EPS), the extrusion manufacturing process gives XPS a uniform, dense structure without air pockets between its cells. This makes it highly resistant to moisture, exceptionally strong, and gives it a superior, long-lasting insulating performance.
How XPS is manufactured
The production of XPS involves an extrusion process that results in its defining closed-cell structure.
- Mixing: Polystyrene crystals are blended with additives and a blowing agent.
- Melting and extrusion: The mixture is heated into a thick liquid and then forced through a die.
- Expansion and cooling: As the material exits the die, it expands and cools into a continuous sheet of rigid foam.
- Finishing: The foam is then cut and profiled into boards of various thicknesses and dimensions.
Key properties
The unique manufacturing process gives XPS foam several key benefits over other foam insulation products.
- High compressive strength: XPS foam can withstand heavy loads without deforming, making it ideal for insulating floors and roofs under heavy pressure.
- Superior moisture resistance: The tightly packed, closed-cell structure prevents water and water vapor from penetrating the foam. This is particularly important for applications where the insulation will be in contact with damp or wet environments, such as below ground.
- Excellent thermal performance: XPS has a higher and more stable R-value (a measure of thermal resistance) per inch compared to EPS because of its closed-cell composition. This allows for a thinner installation to achieve the same insulation value.
- Durability: Its rigid composition and moisture resistance ensure that its thermal and mechanical performance will last for the lifetime of the building.
Common applications
XPS foam’s combination of strength and moisture resistance makes it a highly versatile building material.
- Floors: Used as underlayment for underfloor heating systems and beneath concrete slabs, especially in load-bearing applications.
- Roofs: Suitable for insulating flat and inverted roofs, which are exposed to harsh conditions.
- Walls: Serves as insulation for exterior walls, below-grade basement walls, and cavity walls.
- Specialty uses: Also found in refrigerated vehicles, cold storage facilities, composite doors, and craft projects.