Call our Team

1 300 888 972
Mon - Fri 8AM - 4PM
Australia Wide Delivery
Expert Advice
20 years experience


Isolite® is the brand name for RMAX block moulded flame retardant modified grade of EPS (expanded polystyrene).

It is a closed cell, resilient, lightweight rigid cellular plastics material produced in a range of densities between 10 kg/m3 and 35 kg/m3.

The main applications for products manufactured from Isolite® are:
•    thermal insulation systems (wall, roof and sub-floor)
•    rendered external cladding (see Note)
•    ceiling panels and other decorative surfaces
•    void fillage and blockouts
•    pipe insulation
•    protective packaging
•    floatation and buoyancy applications

Note: Rendered cladding must be done to a minimum standard using cement based polymer modified render and alkali resistant fibreglass mesh.

Manufacturing Process

Expanded polystyrene is supplied as plastic (Polystyrene) beads in which an expanding (or blowing) agent, usually pentane, has been dissolved. In the presence of steam the thermoplastic polystyrene softens and the increasing vapour pressure of the expanding agent causes the beads to expand up to 50 times their original volume. During this stage the degree of expansion is controlled to achieve the desired density.

From the pre-expander the beads are gently transported to large hoppers for ageing. The time of ageing is set to cool and stabilize the beads and allow for infusion of air to replace the expanding agent in the cells.

After conditioning, the beads are charged into a closed mould where they are further expanded and fused together by steam heating.

The freshly moulded blocks of Isolite® are passed through temperature controlled ovens to remove moisture and expanding agent, and to provide blocks of constant dimensional stability and dryness.

Environment Aspects

RMAX Isolite® EPS contains no hydrofluorocarbon (HFC) or hydro chlorofluorocarbon (HCFC) blowing agents that might cause depletion of ozone in the upper atmosphere. The Ozone Depleting Potential of RMAX Isolite EPS is zero (ODP=0).

When used as insulation and cladding EPS provides a reduction in energy use and costs for cooling in summer or heating in winter. Over the lifetime of its use in such applications EPS is carbon negative – saving much more in energy than was used to make the raw material.

EPS is 100% recyclable – RMAX recycles off-cut and unused material into finished products whilst maintaining the required physical properties of those products.

Waste EPS can also be processed into raw materials for other processes. RMAX re-processes EPS into compact Polystyrene which is then used in plastic products from picture frames to garden seats and fence posts. Some EPS recycle material is used for soil conditioning and aeration.

For more information on EPS and the environment please contact your nearest RMAX office.

Manufactured to a Standard

Isolite® EPS is manufactured to AS 1366 Part 3 - 1992, Rigid Cellular Plastic Sheets for Thermal Insulation, Rigid Cellular Polystyrene, in six classes. The standard designates a colour to identify each of the six classes:


The standard specifies the minimum physical property limits for each of the six classes (See Table 1) and methods for determination of compliance.

Quality Control

To meet with the compliance requirements of the standard, the RMAX quality control system monitors and controls each stage of the manufacturing process and assures that Isolite® conforms to AS 1366 Part 3 - 1992 within 95% confidence limits by on site testing of density and key physical properties.

Comprehensive physical testing for product development and quality assurance is carried out in the company’s own laboratory, which is NATA accredited.

Properties of Isolite®

The physical properties are primarily determined by the moulded density for well made oven cured EPS.
(See Fig.1 to 4).


these properties will be affected by raw material and manufacturing variations, and for this reason AS 1366 Part 3 - 1992 specifies the classes in terms of performance properties rather than density.

The standard lists Nominal Density for each class (See Table 2), but these densities should be regarded as a guide only as the physical properties shown in Table 1 may be achieved by EPS of other densities.

Mechanical Properties

The density dependency of the main physical properties of Isolite® can be seen in (Fig.1 to 4):
Compressive stress, Cross-breaking strength (flexural strength), Tensile strength and Shear strength.

Compressive Creep

It is common to report only the compressive stress at 10% deformation but the latter is often taken from complete stress-strain curves as shown in (Fig.5). Although it appears to deform elastically over a range of comprehensive loads, Isolite® that has been stressed will, with the release of all stress, retain some permanent deformation.

(Fig.1 to 5) can be useful for short term loads where some deformation is acceptable. For long term loads (Fig.6), showing compressive creep under constant loads versus time, should be used.

It should be noted that compressive strength in AS 1366 Part 3 - 1992 is a performance characteristic at 10% deformation and should not be taken as a universal design loading recommendation.

Floatation Properties

The density of Isolite® is low compared with water, with a nominal density range from 10 to 25 kg/m3 compared with water at 1000 kg/m3. The water buoyancy per cubic metre of Isolite® is determined by subtracting its kg/m3 density from 1000. The result is the weight in kilograms which a cubic metre of Isolite® can support when fully submerged in water.

Thermal Properties

The low thermal conductivity (k value) of Isolite® characterises its exceptional insulating properties.
(See Fig.7).

As (Fig.8) shows, EPS has a remarkably high R-value compared with most other insulating materials used in similar applications.

Isolite® EPS gains its thermal resistance from the stabilized air trapped within its cellular structure; it contains no hydrofluorocarbon (HFC) or hydro chlorofluorocarbon (HCFC) blowing agent that might cause depletion of ozone in the upper atmosphere.


Design Thermal Properties

As AS 1366 Part 3 - 1992 is a minimum conformance standard, the thermal resistances quoted will be achieved, as a minimum, in 97.5% of cases in a statistical sample, when tested at a mean sample temperature of 23ºC.

Thermal resistance varies with mean insulation temperature, where mean insulation temperature is the average of the temperature on either side of the insulation.

For design purposes the average thermal resistance is a better guide than the minimum thermal resistance.

A full listing of design thermal conductivity values for each class of EPS at differing mean temperatures is shown on Table 9.

Low Temperature Operation

Isolite® does not become brittle at sub-zero temperatures. The testing of specimens at -75ºC for 48 hours demonstrates no loss of impact resistance compared with specimens tested at +23ºC.

Isolite® is able to withstand temperature cycling and thereby assure long term performance without the loss of structural integrity of physical properties; core specimens taken from 20 year old freezer rooms show virtually no deterioration.

Unlike some other insulating materials, the k value of Isolite® decreases at lower average mean temperatures (See Fig.9).

High Temperature Operation

The effect of elevated temperatures on the mechanical properties is an accelerating decline in the values shown in (Fig.1 to 5) until at approximately 85ºC the so-called zero strength is reached.

Isolite® should not be continuously exposed to temperatures in excess of 80ºC as expansion and blistering may occur.

Effect of Moisture on Thermal Conductivity (k value)

The dimensional stability and mechanical properties of Isolite® are not affected by water but because absorbed water will increase the k value, as with all insulating materials, care should be taken in designing insulated structures to take account of water and water vapour that may be present.

While Table 3 shows that certain amounts of water are absorbed by EPS under various conditions, Table 4 demonstrates that the loss of R values in EPS as a result of this moisture absorption is minimal. Overseas research [Ref(i)] has revealed that the decay in thermal resistance caused by moisture is considerably less for EPS than for either extruded polystyrene foam or cellular glass. (See Fig.10). As with other building materials care should always be taken to keep Isolite® dry before and during installation.



Water Vapour Transmission Properties

Although Isolite® has a low water vapour transmission rate it is not considered a vapour barrier. This breathability characteristic reduces any tendency towards the formation of vapour dams.

As (Fig.11) shows, of all the material used for insulation purposes, EPS is one of the most resistant to the adverse affects of moisture.

In applications where high humidity and high temperature differentials are likely a vapour barrier should be installed. Normally the vapour barrier should be installed on the warm side of the structure with the insulation as near as possible to the cold side.

Acoustic Properties

Because Isolite® has a closed cell structure, it offers only a limited absorption of airborne sound. Structure borne sounds, transmitted through such structures as walls and pipes, may be effectively isolated by the use of floating floor systems. For this type of sound insulation, Isolite® with the required dynamic stiffness can be obtained by compressing the sheets by 50 to 60 percent and then allowing them to recover to 80 to 90 per cent of their original thickness.

Chemical Properties

Table 5 shows Isolite® is resistant to virtually all aqueous media including dilute acid and alkalis. In addition, it is resistant to water-miscible alcohols such as methanol, ethanol and i-propanol, and also to silicon oils. Isolite® has limited resistance to paraffin oil, vegetable oils, diesel fuel and vaseline.

These substances may attack the surface of Isolite® after long term contact. Isolite® is not resistant to hydrocarbons, chlorinated hydrocarbons, ketones and esters.

Paint containing thinners and solutions of synthetic adhesives naturally fall in to the same category, and this should be taken into account in any painting or bonding operation.

Anhydrous acids such as glacial acetic acid or fuming sulphuric acid destroy Isolite®.

Prolonged exposure to UV light causes yellowing and embrittlement of Isolite®, which should therefore be protected from direct outdoor exposure.

Download: Table 5: Isolite® Chemical Resistance Table.pdf

Electrical Properties

The electrical characteristics of Isolite® (See Table 6) and air are similar. This applies to arc resistance, as well as other electrical properties. The EPS melts about the path of an arc as soon as the arc penetrates it. Dielectric loss of Isolite® is quite low.

Flammability Properties

Expanded polystyrene products are combustible and should not be exposed to open flame or other ignition sources.

As with all other organic material, insulation products must be considered combustible and to constitute a fire hazard if improperly used or installed. The material contains a flame retardant additive to inhibit accidental ignition from small fire sources. Table 7 shows test results for Isolite® and other common building materials to provide a guide as to how these products compare.

Resistance to Fungi and Bacteria

Fungus attack has not been observed on Isolite®, and it does not support bacterial growth. Surface spoilage (in the form of spilt soft drink, sugar, etc.) can however supply the nutrient for fungal or bacterial growth.

Resistance to Ants, Termites, Rodents and Marine Borers

Since it has no food value, Isolite® does not attract ants, termites, or rodents, however, it is not a barrier to them. Ants, termites and rodents will chew through Isolite® to reach food or establish a comfortable home.

Marine borers can attack EPS, as they do wood and Isolite® should be protected by an anti-fouling paint over a suitable primer.

Coefficient of Linear Thermal Expansion

The coefficient of linear thermal expansion for Isolite® is 6.3 x 10-5 m/m deg K. It is constant across the range of densities used in Isolite products.


The heat of combustion of solid polystyrene polymer is 40,472 kJ/kg; combustion products are carbon dioxide, water, soot (carbon), and to a lesser extent carbon monoxide.

A CSIRO report [Ref (ii)] comments that the toxicity of gases associated with the burning of EPS is no greater than that associated with timber. Extensive research programs have been conducted overseas [Ref (iii)] to determine if thermal decomposition products of EPS present a toxicity hazard. The test results have revealed that the toxicity of the decomposition products appears to be no greater than for wood and decidedly less than other conventional building products.

Storage and Handling

For recommendations on storage and handling Expanded Polsytyrene users should obtain a copy of ‘Recommendations for Storage and Handling of EPS’ available from any RMAX office.


(i) Wayne Tobiasson and John Ricard, US Army Cold Regions Research and Engineering Laboratory, ‘Moisture gain and its thermal consequences for common roof insulations'.
(ii) P.R. Nicholl and K.G. Martin, 'Toxicity considerations of combustion products from cellular plastics'.
(iii) H.Th Hofmann and H. Oettel, 'Comparative toxicity of thermal decomposition products'.

Thermal Conductivity Design Values (W/mK) k value

(a) Determine mean temperature of insulation in ºC
To = Temperature on outside surface of insulation
Ti = Temperature on inside surface of insulation
T mean = To + Ti
Select the class of EPS from AS 1366 Part 3 - 1992
Look up relevant k value in the table for the mean temperature
in ºC Thermal conductivity quoted in W/mK

Download: Table 9: Thermal conductivity W/mK (k values).pdf