XPS Insulation

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Within the polystyrene insulation lineage, XPS insulation stands as the paramount choice for thermal insulation. Its thermal performance markedly exceeds that of its counterpart, EPS. What marks the difference between these two materials is the way in which they are manufactured. XPS is a product of extrusion: a process which endows XPS insulation boards with their smooth skin and closed cell structure. 

Boasting low thermal conductivity, high compressive strength and impressive moisture resistance, XPS boards are suitable for various applications, from wall and roof insulation to below-grade and under-slab uses. Their closed-cell design ensures they can be used as below-grade or damp-area insulation. 

Kingspan is the main manufacturer of XPS foam insulation board in the UK. 

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What is XPS Insulation? 

XPS insulation (extruded polystyrene insulation) is a type of rigid foam insulation made from polystyrene. 

Characterised by its closed-cell structure, XPS provides an effective barrier against moisture and maintains consistent insulating properties over time. 

It's commonly used in building and construction for thermal insulation, often seen in wall insulation, roofing layers, and foundation applications due to its durability and resistance to moisture.

Typically, an XPS insulation material has a thermal conductivity in the ballpark of 0.033 W/mK, which is not as efficient as PIR. 

As a result, a marginally thicker layer of XPS is needed to reach comparable thermal insulation levels. In an industry that often touts the benefits of ultra-thin insulating solutions, this may appear to put XPS at a slight disadvantage. 

However, it's worth noting that XPS insulation doesn't rely on foil facings to deliver its specified performance.

Where is XPS Used? 

XPS boards can handle a significant amount of load without deforming, making them ideal for applications requiring high compressive strength, like beneath concrete slabs or in foundation walls.

XPS can also be employed in the following applications: 

  • Above-grade insulation applications (walls, attics, ceilings, floors, and roofs)
  • Below-grade walls (basements and foundation)
  • Underslab insulation 
  • Cavity wall insulation 
  • Flat and pitched roofs
  • Deck insulation 
  • DPC insulation
  • Insulation backing where EPS won't suffice

XPS Benefits

  • High compressive strength
  • Features a smooth closed cell surface
  • Low water absorption rate
  • Compatible with various construction material
  • Dense structure - can withstand long-term exposure to moisture without decomposing 
  • Closed-cell structure minimises air movement through the insulation, enhancing energy efficiency

How is XPS Made? 

XPS insulation is produced by mixing polystyrene pellets with various additives and blowing agents. This mixture is then heated to a high temperature, turning it into a thick liquid. The liquid is extruded through a die and expands as it cools, forming a rigid foam board. The extrusion process creates a uniform, closed-cell matrix that gives XPS its distinctive properties.

XPS Environmental Considerations

The GWP of XPS is higher compared to some other insulation materials. This is partly due to the blowing agents used in its production, which can have a higher global warming potential. These agents are critical for creating the foam's structure but contribute to greenhouse gas emissions both during manufacture and as they slowly escape from the material over time.

Additionally, like other polystyrene products, XPS is not biodegradable and can be challenging to recycle, contributing to concerns about plastic waste.

Extruded Polystyrene XPS Board Storage

Store in a dry location, ensure the original packaging remains intact, and avoid excess heat and UV light exposure.

Frequently Asked XPS Insulation Questions

How Do I Cut XPS Insulation Board? 

A hot wire cutter is an electric device designed for slicing through polystyrene insulation materials like EPS and XPS foams. 

Rather than employing a sharp edge, this tool utilises a heated wire that melts the insulation, ensuring precise and clean cuts through the foam boards.

How Does XPS Compare to EPS (Expanded Polystyrene) Insulation?

While both XPS and EPS are types of polystyrene insulation, XPS typically has a higher resistance to moisture and often offers better compressive strength. However, XPS is generally more expensive than EPS.

Can XPS Insulation Boards Be Used Below Ground?

Yes, XPS is commonly used in foundation applications because of its ability to resist moisture and maintain its insulating properties when in contact with the ground.

How Do You Install XPS Insulation Boards? 

XPS boards can be cut to fit and attached using adhesive or mechanical fasteners, depending on the application. Always follow manufacturer guidelines for installation to achieve optimal performance.

Are XPS Insulation Boards Fire Resistant? 

While XPS is combustible, many XPS products are treated with flame retardants to slow the spread of flames. 

It's always recommended to use a fire barrier in conjunction with XPS for safety.

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Difference Between XPS and EPS Insulation

Insulation Material Types and Their Uses

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