Extruded Polystyrene

Extruded polystyrene is normally manufactured by a vacuum process, although some is blown with CFCs. It is slightly denser and therefore slightly stronger in compression than expanded polystyrene, but has a lower thermal conductivity. It has a closed-cell structure with very low water-absorption and vapour-transmission properties. Extruded polystyrene is available with densities ranging from 20-40 kg/m3. Extruded polystyrene is widely used for cavity wall and pitched roof insulation. Because of its high resistance to water absorption, extruded polystyrene may be used for floor insulation below the concrete slab and on inverted roofs where its resistance to mechanical damage from foot traffic is advantageous. Extruded polystyrene is also available laminated to tongued and grooved moisture-resistant flooring grade particleboard for direct application to concrete floor slabs, and laminated to plasterboard as a wallboard. (The thermal conductivity of extruded polystyrene is typically 0.025-0.027 W/m K.)

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