Expanded Polystyrene (EPS)

Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam 98% of which contains air trapped within fine cells during manufacture. Unlike other building materials, where increase of strength means higher thermal conductivity and lower thermal performance, thermal qualities of expanded polystyrene improve with its strength (with its density).

Other advantages of expanded polystyrene insulation are: high resistance to biological corrosion, high resistance to the effects of moisture and water vapour (vapour permeability less than 2%).

EPS polystyrene is unaffected by insects and will not support the growth of fungi, moulds or bacteria. The material is non toxic and easy to cut and work with.

In terms of fire performance EPS polystyrene is flammable - however it does not contribute to the spread of flame and goes out after a short while. Expanded polystyrene should not be used in areas exposed to temperatures above 80°C. The material is not resistant to UV waves and if exposed to direct sun light for prolonged periods turns yellow losing its strength and begins to crumble.

The classification parameter of EPS polystyrene is its vertical compressive strength measured at 10 percent deformation or yield, e.g. EPS70 means expanded polystyrene with a compressive strength of not less than 70kPa.

Compressive strength of polystyrene is directly related to its flexural strength. Flexural strength of a material is defined as its ability to resist deformation (bending) under load and in case of EPS 70 polystyrene equals not less than 115kPa (minimum flexural strength of all EPS polystyrene products is 50kPa).

The mechanical strength of EPS polystyrene insulation determines its application that is why compressive stress has formed the basis for classification of polystyrene insulation products.

Classification of EPS polystyrene insulation

• EPS 50 – typically used where there is no mechanical load present e.g. cavity walls
• EPS 70 – suitable for applications subject to low mechanical loads e.g. external walls of the building, pitched roof under rafters, insulation of walls with cladding ventilated by air slots
• EPS 100 – suitable for applications subject to medium-high mechanic loads - insulation of solid ground supported floors, roofs and basements of the building
• EPS 200 – used where high mechanic loads are present e.g. floors in garages
• Compressible Fill - a low density expanded polystyrene board (EPS) used to reduce the pressure exerted on reinforced concrete ground beams (100mm – 300mm Claylite boards) or on the vertical face of concrete foundations (50mm – 75mm Claylite boards), caused by the change in the moisture content within the clay soil (clay heave) and therefore its expansion and shrinkage during the life of the structure

Polystyrene is manufactured in many forms and can be purchased as:

• Rigid boards – with square or bevelled edges (tongue and groove or overlap joint)
• Flexible boards - used for under floor heating systems
• Boards faced with bitumen layer – for insulating pitched and flat roofs in the situation where roof covering is bonded directly to the insulation layer
• EPS Cavity Closers – used to fill wall cavity around windows and door openings
• EPS granules – blown in insulation for insulating areas with restricted access

Advantages of using EPS polystyrene insulation products:

• Durability of insulation – after 50 years the mechanical strength and thermal performance of EPS polystyrene does not degrade
• Ease of processing (cutting etc.) and transport
• EPS insulation can be installed during any season of the year regardless of humidity and temperature
• The material is non toxic and easy to cut and work with
• EPS polystyrene boards are resistant to the effects of moisture
• EPS is characterised with high resistance to biological corrosion
• EPS polystyrene is unaffected by insects and will not support the growth of fungi, moulds or bacteria

Precautions

• In any case, EPS polystyrene foam must be protected from coming into contact with solvent-based paints and adhesives which trigger the chemical reaction causing the EPS foam to melt.
• Polystyrene EPS must not be exposed to direct sun light for prolonged periods to prevent its surface from degrading and eventually turning into dust; therefore EPS foam should be stored under covering and in the shade at all times.
• Whenever maintaining a flat surface and eliminating thermal bridges is crucial EPS polystyrene should be mounted with tongue and groove jointing.

Insulation Cart offers EPS polystyrene insulation in a range of thickness to suit all applications. Our EPS boards come from recognised manufacturers - Kay-Metzeler, Jablite - all available with 1-2 days delivery within UK and 10-15 days within EEC.