Polystyrene Insulation

Whilst they might look light and fluffy, Polystyrene boards have excellent compressive strength, making them ideal for both floors and roof applications. Two of the most popular polystyrene insulation solutions you’ll come across when looking into rigid foam insulation are expanded and extruded polystyrene (EPS and XPS). Both materials have a closed-cell structure and are made from the same base polystyrene resin. At Materials Market, we stock both: expanded polystyrene (EPS) and extruded polystyrene (XPS). 

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What Is Polystyrene Insulation?

Polystyrene insulation is surprisingly rigid, despite its lightweight composition. Polystyrene foam insulation is 95-98% air, due to the thousands of pockets of air trapped inside the material. Expanded polystyrene foam and extruded polystyrene foam are the two most popular types of this insulation. 

Lots of people invest in polystyrene boards to improve the thermal envelope of their homes. Any type of bulk insulation works on the same principle, no matter what material is used. The aim is to create as many air pockets as possible inside the material. The more air you can trap inside your material, the more effective your material will be at resisting heat flow.

Expanded Polystyrene Insulation

When compared to other rigid insulations, Expanded Polystyrene Insulation Board (otherwise known as EPS) is, without doubt, the most cost-effective. This is due to the fact that it is less dense and cheaper than XPS as it is less thermally effective. Unlike XPS, EPS is not a closed-cell insulation board (whilst it has a closed-cell structure) meaning it allows water vapour/moisture to penetrate over time.

Despite its performative inferiority to more premium brands of thermal insulation, EPS exhibits consistent thermal performance in an extensive range of building insulation applications such as floor, wall and loft applications. These boards are the perfect choice for meeting current building regulations and U-value requirements with little to no effort. Not only do they possess high load-bearing capacity but they are also moisture resistant and unaffected by bacteria, moulds and fungi.

EPS insulation is predominantly used as floor insulation and in external wall insulation systems. Most people invest in Jablite insulation boards when they want to reduce the amount of heat they lose through their floorboards or floor tiles. EPS insulation is available in a range of thicknesses from 25mm to 100mm, which makes it suitable for a range of insulation projects. 

Extruded Polystyrene Insulation

Extruded polystyrene insulation (often referred to as XPS) is manufactured, as the name would suggest, through an extrusion process. Kingspan is the main manufacturer of this insulation in the UK. Extruded polystyrene insulation (XPS) is manufactured using a process of extrusion. This process results in a closed-cell structure that boasts smooth, dense skin on both faces. The closed-cell structure of extruded polystyrene (XPS) prevents water penetration, thus providing long-term strength and durability.

Kingspan GreenGuard boards have a thermal conductivity of 0.034 W/mK. As such, XPS foam is marginally more effective than EPS foam as a thermal insulator. It is tough when it comes to insulation yet gentle when it comes to the environment, as the blowing agent used to manufacture it has zero ODP (Ozone Depletion Potential) and low global warming impact.

GreenGuard insulation is high-performing in its versatility and can be installed in both residential and commercial properties. You can install Kingspan GreenGuard XPS foam in inverted roofs, basements, car parks, and even underneath industrial cold-flooring. GreenGuard foam boards have a compressive strength of 300 kPa, meaning these boards will not lose their thermal properties when placed under pressure. We stock a wide range of extruded polystyrene insulation thicknesses from 30mm to 120mm.

Polystyrene Insulation Compressive Strength

The numbers in the titles of each expanded polystyrene board refer to the compressive strength. The EPS70 range has a compressive performance of 70 Kilopascal (kPa). When buying polystyrene foam insulation, it is important to think about compressive strength. The greater the compressive strength of the material, the more load resistant it is. External pressure like footfall and vibrations will not impact the longevity of EPS boards that have high compressive strength. 

Like EPS, XPS foam boards have numbers in the title. All the XPS products in our range have a compressive strength of 300kPa. They are far better for commercial spaces than EPS. We recommend extruded polystyrene insulation for people who want to insulate heavy floors and roofs.

Frequently Asked Polystyrene Insulation Questions

Is Polystyrene Insulation a Good Insulator?

Polystyrene boards have a thermal conductivity value between 0.034 and 0.038 W/mK. XPS foam boards are more efficient thermal insulators than EPS insulation boards.

Polystyrene does not deliver the best thermal conductivity values on the market. Phenolic insulation has a thermal value of 0.018 W/mK, which makes it the most efficient material available for thermal protection. Polystyrene is more suited to applications where thermal values are less of a consideration, but where compressive strength is important.

Are Polystyrene Insulation Boards Good For Compressive Strength?

Polystyrene insulation boards have excellent compressive strength. Kingspan GreenGuard boards have a compressive strength of 300 kPa, whereas EPS70 jablite polystyrene boards have a compressive strength of 70 kPa. 

The higher the compressive strength, the longer the material maintains its properties. GreenGuard boards perform well when they are installed in heavy roof structures and underneath heavy floors. Lots of commercial property owners invest in polystyrene foam because it maintains its thermal properties despite heavy footfall. 

Are Polystyrene Insulation Boards Sustainable?

Unlike XPS, EPS can be constructed with recycled content, making it the more environmentally friendly option of the two. However, this sustainability does not come without its disadvantages. The voids between the polystyrene beads of EPS also make it more permeable and susceptible to water absorption. And with the absorption of water, comes the dreaded decrease of R-Value (dulling down its already quite low thermal properties). 

Resisting water is critical for high-performance insulation due to the fact that water is an excellent conductor of energy. Water ingress will ultimately hurt the overall thermal effectiveness of the board since water allows energy to short circuit or bypass its way through the board’s structure; reducing the overall effectiveness of thermal performance.

It should be noted then, that EPS’ potential to absorb water is 10 times greater than XPS, which does not absorb water at all, due to its closed-cell structure. This enables it to maintain insulating power in the presence of water.