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Isolite® SL and Isolite® S

Isolite® is closed cell expanded polystyrene, which produces a high thermal resistance per unit of thickness. It is resilient and lightweight and manufactured to comply with AS 1366 Part 3 - 1992.

Product Types

Computer Cut Sections


When it is not possible to use pre-cut pipe, computer cut shaped sections of insulating foam can accurately be installed around the largest of vessels.

Flat V-Cut Sheet

V-scored sheets of insulating foam are available for large vessels. Computer calculated V-cut channels are cut into sheets, ensuring a perfect insulation fit. ThermaLock® flat V-cut sheets provide coverage to large areas with a minimum number of sheets. These sheets can be transported flat, reducing the possibility of damage in transit.

Determining Insulation Thickness

Insulation thickness is normally determined by the need to prevent condensation on the outer surface of the finished insulation.

Two ways to determine the thickness of insulation are:

  • using the nomogram provided below
  • providing specific information to RMAX for calculation using an RMAX computer-based formula.

The details of each of these options follow;


Insulation thickness to prevent condensation for cold pipelines and flat surface in still air (assumed emissivity = 0.9). It should be noted that condensation cannot be prevented in conditions of 100% relative humidity, regardless of insulation thickness. An insulating thickness which allows only a 1°C temperature difference between the surface and ambient air might be considered an ultimate practical limit. This temperature difference would prevent condensation at 95% relative humidity for all normal ambient temperature.


Given an air temperature of 15ºC and R/H = 85%, where the temperature difference between the pipe and air 33ºC, the thickness of E.P.S. pipe insulation required (k = 0.036) for a pipe of nominal 75mm bore can be read from the nomogram as ~ 45mm.


RMAX Computer Calculation

This service is available to all RMAX customers and requires clients to supply the following information:

  1. Cold surface temperature °C
  2. Surrounding air temperature °C
  3. Relative humidity of surrounding air
  4. RMAX insulation material selected
  5. Finished surface exposed to surrounding air
    e.g. aluminium, galvanized steel, zincalume, zincaneal
    Base insulation or dark coloured paints or mastics
  6. Wind speed, if not assumed still air
  7. In the case of pipes, outside pipe diameter




Physical Properties

RMAX rigid insulation foams are manufactured to 1366, Parts 1,2,3.

Thermal Expansion

In designing insulation systems the thermal expansion of all materials must be taken into account. This may necessitate the use of expansion joints.

Coefficient of Thermal Expansion m/m°C

Isolite® class SL
(Approx 13.5g/l)  63x10-6


Like many materials used in construction EPS is combustible, and may constitute fire hazards if improperly used or installed. This material contains a flame retardant additive to inhibit accidental ignition from a small flame source.

Comparative early fire hazard testing of some materials to AS 1530.3 – 1982.

Material  Ignitability index (0-20) Spread of flame index (0-10) Heat evolved index (0-10)  Smoke developed index (0-10)
Isolite® 12 0 3 5
Isothane® 18 10 4 7
Korthane® 17 10 4 7
Isothex® 16 0 0 5
Softboard  16 9 7 3
Oregon 13 6 5 3
Bluegum  11 0 3 2
Radiata pine 14 8 9 3
Hardboard 14 7 9


Expanded polystyrene (EPS) is chemically inert and is non toxic. Gases released during combustion are predominantly carbon dioxide and to a lesser extent, carbon monoxide. A CSIRO report comments that the toxicity of the gases associated with the burning of EPS is no greater than that associated with timber.

Adhesives and Coatings

A range of protective coatings and adhesives suitable for use with the insulating foams in the RMAX range is available. However, protective coatings and adhesives containing aromatic base solvents must not be used with Isolite® foam. Prior to application of any new adhesives or coating, a test application should be made to confirm compatibility.

Effects of Sunlight

The surface of expanded polystyrene foam will be degraded by sunlight. For this reason, they should not be left exposed to the sun for extended periods of time prior to installation, or the application of adhesives and coatings.

Material which may be exposed to sunlight should be protected by a white polyethylene film or other suitable light coloured covering. Sunlight degradation can usually be recognised by discolouration. Any degraded material should be removed by brushing or air blasting before material which requires adhesion to the foam is applied.

Material Specification

  • Insulation shall be longitudinal shiplap section (ThermaLock®).
  • Expanded polystyrene, class SL, to AS1366 Part 3  (Isolite®, Class S)
  • Quality schedule
  • Pipe diameter
  • Minimum insulation thickness