Elastomeric foam — theory, properties and applications

Elastomeric foam is a rubber material that has been foamed by heat into a soft, insulating membrane with fully closed cells. The closed cells give the material a very high vapour tightness and good insulating capacity, especially in the low-temperature range, where condensation can be a problem.

Elastomeric foam is produced in an extruder, where approx. 40 different granulated raw materials — including a blowing agent — are mixed and forced through a pressure chamber by a screw. The mass is fed out through interchangeable die openings that determine the tube's inside diameter. The product then passes through a curing oven of up to 65 metres, where the material expands in a controlled way to at least 3–4 times its original size in both diameter and length.

Standard AF-Armaflex is used from −50 °C to +110 °C (but only up to +85 °C if the joints are finished with tape). HT-Armaflex has a maximum service temperature of +150 °C and the same minimum temperature of −50 °C. Armaflex Ultima is the first flexible cold insulation with the fire classification BLS1D0 and the fire-stopping property EI30–EI120; this variant is recognisable by its blue colour.

The lambda value (λ) indicates a material's thermal conductivity measured in W/mK. Elastomeric foam has a lambda value of 0.033 W/mK, while mineral wool is typically 0.037 W/mK, and foamglas and paper insulation 0.040 W/mK. PU foam is better than elastomeric foam. The insulating performance of elastomeric foam surpasses most known materials, with the exception of polyurethane foam.

The lower the lambda value, the better the material insulates.

Three factors are always mandatory when calculating insulation thickness: medium temperature (the pipe's contents), ambient temperature and relative humidity. The manufacturer provides the calculation programme Amwin. As an example, insulation class 2 at a medium temperature of 67 °C, an ambient temperature of 18 °C and a relative humidity of 55 % requires an elastomeric foam thickness of 20 mm — compared with 30 mm for mineral wool.

DS452, in force from 31 May 2014, regulates the thermal insulation of building services installations (heating, ventilation, cooling, solar heating pipes etc.) with operating temperatures from −40 °C to +650 °C. There are six insulation classes (1–6) with maximum permitted heat loss from 1.17 W/m² (class 1) down to 0.22 W/m² (class 6); class 0 requires no insulation. The standard does not apply to district heating supply pipes up to the main valve, building structures, cold stores, boilers or heat pumps.

Warm air can hold more water vapour than cold air: at 30 °C approx. 30 g water/m³, at 20 °C approx. 17 g/m³ and at 7 °C only approx. 7 g/m³. When the air is cooled to the dew point temperature, it is 100 % saturated and condensation occurs. For example, with a 6 °C pipe (mains water), 22 °C ambient temperature and 85 % relative humidity, the dew point is approx. 19.4 °C, corresponding to 15.7 mm into the insulation. An insulation thickness of 20 mm ensures that the dew point is moved out into the insulation and therefore does not reach the pipe surface.

The mu value (μ) of elastomeric foam, which indicates the material's ability to resist vapour, is up to 10,000 — among the highest known. Because the cells are fully closed, the material retains its integrity even with minor surface damage, unlike mineral wool products with aluminium foil facing, where even a small hole can compromise condensation protection. Correct section bonding ensures 100 % tightness against moisture spreading beneath the pipe.

Because the outer surface area of an insulated pipe is larger than the surface of the uninsulated pipe, the heat has to be transferred over a larger area. The smaller the pipe diameter, the greater the difference. For an 18 mm pipe with 13 mm insulation, the outer surface is 2.44 times larger than the pipe surface, while a 60 mm pipe with the same insulation only gives a factor of 1.43. Smaller pipe diameters therefore require proportionally thicker insulation for the same insulating effect.

Even if the insulation thickness has been calculated correctly, stagnant air in narrow gaps between pipes or between pipes and structures can lead to condensation. The rule is that there must be a minimum distance of 50 mm between the outer surfaces of the finished insulated pipes.

Dusty surfaces must be cleaned with Armaflex cleaner before bonding. Pipe surfaces must also be adequately protected against corrosion — e.g. with anti-corrosion paint — before the insulation is fitted. This is because the moisture in the air trapped under the tube during installation can cause corrosion over time if the surface is not protected.

Armaflex contact adhesive has paint code 3,1 and contains volatile, highly flammable substances. Avoid inhaling vapours and contact with skin and eyes; naked flames and other ignition sources are prohibited. Provide mechanical ventilation or use respiratory protection. Stir the adhesive thoroughly before use, and the system must not be put into service until the adhesive has fully cured — this takes 36 hours. The correct open time is determined with a fingernail test.

To ensure 100 % tightness against moisture migration, the insulation must be section-glued: all longitudinal joints are glued, and gluing is done every 2 metres (corresponding to the tube length) and up against all supports and fittings.

Never use tape alone over supports as a substitute for insulation — there is no insulating capacity in an area covered only by tape.