Extruded polystyrene foam, commonly known as XPS foam, is a high-performance rigid insulation material widely used in construction for its exceptional moisture resistance and compressive strength. This guide explains what XPS insulation is, how it works and where it performs best.
XPS Quick Answers
What is XPS foam?
XPS (extruded polystyrene) is a closed-cell rigid foam insulation board manufactured by extruding polystyrene through a die. It's recognisable by its smooth surface and uniform closed-cell structure, typically available in blue, green or pink colours depending on the manufacturer.
What does XPS stand for in insulation?
XPS stands for "extruded polystyrene". The term describes the manufacturing process where polystyrene is melted and extruded through a die to create foam boards with a completely closed-cell structure.
What is XPS foam made of?
XPS foam is made from polystyrene - a synthetic polymer derived from petroleum. During manufacturing, polystyrene is melted, mixed with additives and a blowing agent, then extruded under pressure to form rigid foam boards with closed cells.
Is polystyrene closed cell?
Yes, XPS (extruded polystyrene) features a completely closed-cell structure with no gaps or voids between cells. This is what gives XPS its superior moisture resistance and consistent thermal performance compared to open-cell or semi-closed-cell insulation materials.
Is XPS foam waterproof?
XPS foam is highly water-resistant due to its closed-cell structure, with water absorption rates typically below 0.3% by volume. Whilst not technically 100% waterproof, XPS resists moisture penetration far better than most insulation materials, maintaining thermal performance even when exposed to moisture.
What is Extruded Polystyrene (XPS)?
Extruded polystyrene is a rigid foam insulation material created through an extrusion manufacturing process. Unlike expanded polystyrene (EPS), which uses beads that are expanded with steam, XPS is manufactured by melting polystyrene and extruding it through a die under pressure.
This process creates a foam board with a uniform, completely closed-cell structure. The result is a smooth-surfaced, rigid insulation board with exceptional compressive strength, minimal water absorption and consistent long-term thermal performance.
XPS vs Polystyrene
Polystyrene is the base polymer material. XPS is the specific type of rigid foam insulation made by extruding this polystyrene. When people refer to "polystyrene insulation" they typically mean either XPS (extruded) or EPS (expanded) polystyrene foam boards.
What is XPS Insulation Material?
XPS insulation material is a closed-cell rigid foam board specifically designed for building insulation applications. As an insulation material, XPS offers:
- Thermal conductivity: Typically 0.028-0.036 W/mK
- Compressive strength: 200-700 kPa depending on grade
- Density: 28-45 kg/m³
- Water absorption: <0.3% by volume
- Operating temperature range: -50°C to +75°C
When to Choose XPS Over EPS
Choose XPS when:
- Moisture exposure is expected (foundations, below-grade walls, inverted roofs)
- High compressive strength is required (floors, parking structures, green roofs)
- Long-term thermal performance in wet conditions is critical
- Dimensional stability under load is essential
- Budget allows for the higher upfront cost
Choose EPS when:
- Application is in dry locations
- Budget is limited
- Lower compressive strength isn't an issue
- Moisture exposure will be minimal
Our XPS Insulation Products
We supply high-quality XPS foam boards from leading manufacturers:
Browse our full range or contact our technical team for specification advice and project support.
