Expanded polystyrene (EPS) is a closed-cell foam manufactured by “expanding” a polystyrene polymer; the appearance is typically a white foam plastic insulation material (the likes of which can be found as merchandise packaging). Extruded polystyrene (XPS) foam is a rigid insulation also formed with polystyrene polymer, but manufactured using an extrusion process, and is often made with a distinctive colour to identify product brand.
Common notion is that polystyrene XPS is a top shelf product with its quality and performance much higher than EPS. This is true if we take into consideration that XPS boards cost twice as much as EPS.
XPS: Extruded Polystyrene EPS: Expanded Polystyrene
But are they always better than ‘old fashion’ EPS polystyrene?
Among numerous advantages related to the use of XPS boards it is possible to note its high thermal performance (low lambda value), minimal water absorption and very high compressive strength. In comparison the cheapest EPS boards are much more water absorbent and less resistant to point loading (lower compressive strength).
Strong EPS boards like EPS200 (with compressive strength of 200 kPa) can achieve thermal conductivity of 0.031 W/m2K. Same thickness of XPS will achieve thermal conductivity of 0.030W/mK - not much difference in thermal insulation properties and at the same time EPS boards are almost half the price of XPS.
Unfortunately compressive strength of expanded polystyrene EPS200 at 10% compression is much lower in comparison to XPS which typically exceeds 300kPa. For that reason XPS would be a better choice for insulating a floor under concrete slab.
Taking into consideration the above in terms of thermal characteristics of the two products, we could risk a statement that for the purposes of family home design, expanded polystyrene EPS200 is strong enough and will meet the building regulation standards. It can be a cheaper and good alternative to XPS in applications like thermal insulation of foundation, terraces and flat roofs.
- Lightweight product easy to cut and shape
- Relatively cheap although some mineral wool insulation products can match its price
- Is characterized with lower water absorption than mineral wool
- Offers relatively high compressive strength
- Good thermal insulation characteristics
- Lightweight and tough product easy to cut and shape
- Characterized with very high compressive strength (typically between 250kPa – 500kPa)
- Very low water absorption characteristics
- Very high thermal insulation properties