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Is Polystyrene Insulation Effective?

At EWI Store, we stock two types of polystyrene insulation, EPS and XPS. These are both ideal for use with external wall insulation systems, offering an effective method of lowering energy bills by improving the thermal performance of properties. Both EPS and XPS are made of polystyrene, so in today’s blog, we’re going to talk a little bit about the difference between the two.

EPS (Expanded Polystyrene)

Expanded Polystyrene Insulation is a lightweight insulation, made of polystyrene foam beads. This means that it is rigid foam, so is ideal for securing to external walls. EPS is 90% air because it is not very dense – the fact that it is made up of lots of small polystyrene beads means that there are lots of tiny air pockets.

This is what makes it a great insulator. Because it’s so lightweight, EPS is perfectly safe to fix to the walls using our dual-fixing method of adhesive and mechanical fixings. The insulation can then be decorated with a thin coat render to protect it against the weather and achieve an aesthetically pleasing finish.

EPS has a thermal conductivity of 0.032(W/mK). This thermal conductivity is maintained for the duration of its lifespan, so once on the wall, you won’t have to replace it further down the line. In terms of building regulations, on a solid wall property, you would need about 90mm of EPS insulation to achieve the required U-value of 0.3(W/mK).

XPS (Extruded Polystyrene)

The real difference between XPS and EPS is in the way they are made. The different processes of manufacture mean that they both have varying levels of performance. XPS is manufactured through an extrusion process, whereby the plastic resin and ingredients are melted together. These are then extruded and expanded to form rigid, closed-cell polystyrene.

Because it’s closed-cell polystyrene, XPS is great for areas that are exposed to higher levels of water – for example, the DPC. Unlike EPS, there’s little chance of the XPS being able to absorb this water, so we recommend the use of XPS if you are planning to insulated right down to below the DPC. XPS also has higher compressive strength, so it’s ideal for this area as it is more exposed and much more prone to experiencing impacts.

In terms of thermal conductivity, XPS has a conductivity of 0.038(W/mK), so you’ll need a slightly thicker 110mm to achieve the required U-value to reach building regulations.  

Although both of these polystyrene insulation materials are of high quality, EPS tends to be more popular than XPS for cost reasons and because it performs slightly better.

If you’re interested in externally insulating your home, get in touch and we can talk you through which of our insulation materials would be best for you.

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