Extruded Polystyrene (XPS) is made by mixing polystyrene and a blowing agent under pressure and then forcing the resultant fluid through a die. As it emerges from the die the fluid expands into a foam, which is shaped before it cools. Extruded is stronger than expanded polystyrene and as such is better suited applications where some load bearing is required such as below ground (for example, in providing an insulation layer in a floor).

Features

• Manufactured from petrochemicals so not sustainable and toxic when burnt.
• High embodied energy.
• Moisture tolerant and relatively durable.
• Versatile, strong and relatively easy to fit.

Performance
Typically has a thermal conductivity or K value in the range of 0.028 – 0.036 W/m.K. (Watts per meter Kelvin ~ lower value is a better result)

Cost
Depending on thickness costs should around £7 a square metre with more specialist flooring products up to £15 a square metre.

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Phenolic foam insulation is made by combining phenol-formaldehyde resin (note the presence of formaldehyde, a hazardous chemical and known carcinogen), a foaming agent and a hardener. When all three are mixed an exothermic reaction causes foaming followed by rapid setting.

Description
Usually now available as rigid boards or panels sometimes as a backing to plaster or chip board.

Features

• Relatively low embodied energy - in comparison to similar products.
• Good fire performance. Very low flame spread, negligible smoke emission and very low levels of toxic gas emission.
• Can be cut and shaped accurately. Often used to closely insulate pipes and can be reused.
• Lightweight, strong and durable in higher density applications.
• Can shrink. If applied as a foam then it can shrink when cured.
• Moisture resistant.

Performance
From 0.018 W/m.K, but typically in the range 0.020 – 0.023 W/m.K (Watts per meter Kelvin ~ lower value is a better result)

Cost
Kingspan Kooltherm is available for around £8 square metre.

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Similar to mineral wool insulation, glass fibre is one of the most common forms of insulation in the UK - everyone knows that rough, itchy, scratchy feel of glass fibre much beloved in our drafty attics. Whilst it has been installed in many homes for at least of couple of decades, this has not usually been done to the same thickness that would now be recommended so a top-up may be in order.

Description
Glass fibre manufacture involves melting the raw materials (which typically include around 50% recycled glass) in a furnace at temperatures in excess of 1500ºC. The resultant molten glass is thrown by centrifugal force to form filaments. These filaments are then aggregated together and the resulting mat of fibres is coated with a resin to bind them together. The resin is then cured in an oven and the mat cut into blankets that can be rolled and packaged.

Features

• High embodied energy.
• Fire proof.
• The fibres can be an irritant.
• Versatile and relatively easy to fit.
• Relatively low cost.

Performance
Blocks of glass fibre have a K value in the order of 0.05 W/m.K. (Watts per meter Kelvin ~ a lower value is a better result)

Cost
Cheap … expect to pay under £2 per square metre including VAT.

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Also know as PIR. Polyisocyanurate is essential a stronger more fire retardant development of Polyurethane. As may be expected it shares many of the characteristics of Polyurethane.

Description
Usually produced as a foam panel insulation, PIR foam panels coated with aluminium are used for the prefabrication of ducts and flues commonly used in heating and cooling systems.
Features

Manufactured [...]

Often abbreviated to PU, Polyurethane is usually applied as a foam insulation sprayed onto the underside of roof rafters.

Description
A complex manufactured compound, polyurethane has traditionally been manufactured from petrochemicals and so has a few green credentials except for those gained from the energy it saves. Recent developments toward the use of polyols derived from [...]