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.

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.

Low temperatures encountered in building construction have no adverse effects on Koolfoam (although the possibility of dimensional changes must be considered) Since Koolfoam softens at high temperatures there are however upper limits to service temperatures: these are summarized in Table 1.The surface of Koolfoam can be briefly exposed to temperatures appreciably higher than 100°C without damage, for instance when the material is bonded with hot bitumen.

Like many organic materials Koolfoam has high linear thermal expansivity: 50-70 MK. Although this value is much greater than those for most tougher building materials (steel, glass, masonry and wood all have vapour in the range 5-12 MK) the forces required to constrain the expansion or contraction of material made from Koolfoam are generally negligible.

Thus expansion is seldom a problem and contraction is only likely to cause difficulty when large drops in temperature are involved, In cold-store construction it is usually necessary to use special jointing systems or contraction joints, since with units 4m long installed at 30°C the unrestrained contraction at -20°C could amount to about 10mm.

Thermal expansion and contraction is reversible, but freshly moulded expanded Koolfoam is also subject to irreversible contraction. This contraction, known as aftershrinkage, proceeds rapidly at first but eventually approaches a limiting value. Once the aftershrinkage is close to the limiting value any residual aftershrinkage is of little importance. For most purposes a residential aftershrinkage of less than 0.2% is acceptable.

Koolfoam board with densities of more than 15kg/m must be stored for some while before the residual aftershrinkage drops to 0.2%. The storage time depends on the manufacturing conditions and the density of the board.

Adverse effects resulting from joints opening by aftershrinkage can be easily avoided by using board with rebate edges or by using two or more layers laid to break joint.

UV and other actinic radiation eventually causes yellowing and embrittlement of polystyrene, so that Koolfoam should be protected from prolonged exposure to sunlight. The embrittlement is confined to the surface of the material, and is not of itself harmful, but it does make the material susceptible to erosion by wind and rain. In practice the usual paints, roofing material, etc, provide the required protection. Koolfoam used indoors is not sufficiently exposed to UV to deteriorate: this is borne out by years of experience with ceiling tiles.

Koolfoam is comparatively inert, and is unaffected by mildly acid or alkaline building materials such as Portland cement, lime or anhydrite. It is however soluble in many organic solvents, and may be damaged by certain commonly used paints, adhesives, wood preservatives, pasting agents, etc. In some cases vapour from these substances can be harmful.

Koolfoam has no nutritive value for micro-organisms, and does not rot. Under certain conditions soiled material may carry fungi etc, but it is not itself attacked. Even soil bacteria has no effect on it.

Rodents and birds occassionally attack exposed Koolfoam, which should be protected by galvanised wire netting if necessary.

Physical Property	Unit	L	SL	S	M	H	VH	Test Method
Compressive at 10% deformation, min.	kPa	50	70	85	105	135	165	AS 2498.3
Cross-breaking strength, min.	kPa	95	135	165	200	260	320	AS 2498.4
Rate of water vapour transmission (max.) measured parallel to rise at 23°C	ug/m2s	710	630	580	520	460	400	AS 2498.5
Dimensional stability of length (max.) at 70°C dry condition 7 days	percent	1	1	1	1	1	1	AS 2498.6
Thermal resistance (min.) at a mean temperature of 23°C (50mm sample)	m2K/W	1	1.13	1.17	1.2	1.25	1.28	AS/NZS 4859.1
Flame propogation characteristics: - median flame duration, (max.) - eighth value (max.) - median volume retained - eighth value (min.)	SD SD percent percent	2 3 15 12	2 3 18 15	2 3 22 19	2 3 30 27	2 3 40 37	2 3 50 47	AS 2122.1
1 W/m.K - 6.93 Btu in/ft2h. °F

Water, seawater, salt solutions	+
Lime, gypsum, Portland cement	+
Caustic soda, caustic potash, strong ammonia, liquid manure, lime wash	+
Soaps and solutions of wetting agents	+
Hydrochloric (to 35%), Nitric (to 50%), and Sulphuric (to 95%) acids	+
Dilute mineral acids and weak acids such as lactic acid, carbonic acid, or humic acids in peaty soils	+
Solid salls, eg. wall saltpetre, artificial fertilizer	+
Bitumen	+
Bitumen omulsion	+
Fluxed or cut-back bitument	-
Tar and products based on tar	-
Milk	+
Liquid paraffin, cooking oils, petroleum jelly, fuel oil	+ -
Silicone oils and greases	+
Lower alcohols, eg. methylated spirit	+
Organic solvents, eg acetone, ethyl acetate, xylene, paint thinners, trichlorethylene, carbon tetrachloride, turpentine	-
Saturated hydrocarbons, eg white spirit, kerosene	-
Gasoline	-
+ Resistant over long periods + - Limited resistance: the cellular material may shrink or suffer surface attack after prolonged action - Non-resistant: the cellular material rapidly collapses or dissolves

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