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Polystyrene is a lightweight cellular plastic foam material composed
of carbon and hydrogen atoms.
It is derived from petroleum and natural gas by-products. Moulded EPS does not involve the use of CFCs.
Polystyrene is sanitary, sturdy, efficient and economical.
EPS meets the performance requirements as set out in the Standards Association of Australia’s AS 1366, Part 3 -
1982 (table 2)
PROPERTIES OF EXPANDED KOOLFOAM
The service life of Koolfoam is virtually unlimited if the material is used knowledgeably. In this point Koolfoam
does not differ from most other building materials, but because its properties are less well known, there is a
greater risk of it being mishandled. This bulletin discusses those properties of cellular material made from Koolfoam
that are relevant to its use in building.
PHYSICAL PROPERTIES
THERMAL INSULATION
Koolfoam is an exceptionally good insulation material. This is the result of its extremely low density and closed
cell structure. It consists of airfilled polyhedral cells, 0.2 - 0.5 mm across, with polystyrene walls about 0.001mm
thick. The polystyrene walls occupy only about 2% of the total volume: the rest is air which is trapped in the
cells and cannot pass from one cell to another. Still air is an extremely poor conductor, so that little heat can
move from one cell to another and the alternative paths along the thin polystyrene cell walls are equally unsuitable
for rapid heat transfer.
The thermal conductivity of cellular materials made from Koolfoam varies with density, and with temperature. Within
the normal density range of material used in building the variation of conductivity with density is comparatively
small.
At 10°C the thermal conductivity of expanded Koolfoam of density 20kg/m is 31-36 mW/m.k. However, in carrying
out insulation calculations for heated buildings it is usual to use the same nominal value for all densities and
temperatures, eg the value of 30 mW.m.K.
The thermal conductivity of expanded Koolfoam does not vary with time, unlike cellular materials whose cells are
filled initially with gases other than air.
MECHANICAL PROPERTIES
Although Koolfoam is easily compressible compared with other types of building material, it is strong compared
with many insulants. The stresses required for a rapid compressive strain of 10% are given in Table 1, they increase roughly
linearly with density. More important is the ability to withstand prolonged compressive stresses. As a rule of
thumb it may be assumed that the prolonged action of stresses less than a quarter of those required for a rapid
compressive strain of 10% will not cause more than 1-2% compression.
Other mechanical properties of Koolfoam are given in Table
1. The values are all dependent of the density of the material.
Unlike many building materials - including many insulants - expanded Koolfoam is neither absorbent nor hydroscopic.
When it is immersed in water for long periods it does take up a small amount of water as there are a number of
interstitial channels. The figures given in Table
1 give an exaggerated picture of the effect, since they were
obtained by immersing 5cm cubes cut from blocks.
In practice the area of cut surface exposed to water would never be so large relative to the volume of the material.
If the material has a moulded skin the water absorption is very low.
Although impermeable to liquid water, Koolfoam is fairly permeable to water vapour. The diffusion resistance factor,
ie the reciprocalof the permeability of Koolfoam to water vapour relative to the permeability of air, is 30-80,
depending on density. Higher values are given by moulded board, which has a denser moulded skin on each side.
Under certain circumstances water vapour can diffuse into Koolfoam and condense within the cells or the interstitial
channels. this can be undesirable, and must then be prevented by using a vapour barrier. The most effective vapour
barrier is metal foil, which has an extremely high diffusion resistance factor, but often it is sufficient to use
less resistance material, such as plastic sheet or roofing felt.
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