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Low Energy House - What is Polystyrene Insulation?

Extruded polystyrene (XPS) is a material with uniformly small closed cells and a smooth skin which make it suitable for a wide range of demanding insulating applications

Polystyrene Insulation  - Extruded Polystyrene - Image Provided by Styrofoam™Polystyrene Insulation Production

Extruded polystyrene is made by mixing polystyrene pellets with various ingredients to liquefy them.  A blowing agent is then injected into the mixture to form gas bubbles. The foaming liquid is forced through the shaping die and, when cooled, it produces a closed cell foam that is rigid and water resistant.

Extruded polystyrene 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. It will withstand continuous temperatures up to 75 degrees C and can be easily worked with normal hand tools.

Polystyrene Insulation - Blowing Agents

In order to comply with EC regulations, blowing gases should be CFC and HCFC free (zero ozone depletion potential) and have low global warming impact.

The most common blowing agent used in this type of insulation production is pentane. Pentane is a hydrocarbon which has similar properties to those of butane and hexane. It is the most volatile hydrocarbon that is a liquid at room temperature. The blowing agent migrates out of the cell structure over a very long period of time and is replaced by air, thereby increasing thermal conductivity of the insulation.

Main Uses of Polystyrene Insulation Board

  • Extruded polystyrene board can be used in ground floor construction, flat roofs, heavy duty floor insulation, panels and other fabrication applications. Because of its high resistance to water absorption, extruded polystyrene can 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 tongue and groove moisture resistant flooring grade particle board for direct application to concrete floor slabs and laminated to plasterboard as a wall board

Physical Qualities of Polystyrene Insulation Board

  • Compressive Strength
    Extruded polystyrene board exhibits high compressive strength. In load bearing applications, the closed cell structure gives the foam great rigidity and makes it highly resistant to compression. Extruded polystyrene is available with densities ranging from 20 to 40 kg/m³.¬†
  •  Polystyrene Insulation - Extruded Polystyrene - Image Provided by Styrofoam™Water Resistance
    Extruded polystyrene board has low water absorption with a natural resistance to rain, snow, frost and water vapour which makes it an exceptionally stable material.
  • Mould Growth
    Extruded polystyrene board has low susceptibility to rot; mould and fungal growth are therefore minimised.
  • Fire
    Extruded polystyrene is combustible if exposed to flame and may burn rapidly. Best quality products contain a flame retardant additive to inhibit accidental ignition from a small fire source. Insulation materials are rigorously tested to British Standards and fire performance data, to meet the requirements of building regulations, is generally available from manufacturers.
  • Recycling
    Extruded polystyrene is non- biodegradable but waste material can be put back into the manufacturing process for reuse.

Thermal Performance of Polystyrene Insulation

Extruded polystyrene has low thermal conductivity allowing board thicknesses to be minimised but still enabling low U-values to be achieved.

The thermal conductivity of extruded polystyrene is typically between 0.027 and 0.025 W/m K at 10 degrees C.

In the UK, when comparing the thermal values of insulating materials, it is important to remember that the best performing material is the one with the lowest thermal conductivity value

About Polystyrene Insulation - Expanded Polystyrene - XPS