Elastomeric foam

Elastomeric foam is a closed-cell, flexible foam made from synthetic rubber. The material is known in English as FEF (Flexible Elastomeric Foam) and is standardised per EN 14304 [iteh.ai EN 14304:2015]. The AMU compendium describes it as "made from approx. 40 different chemical components and elements in a rubber material that, through the application of heat, is foamed into a soft insulating membrane characterised by its completely closed cells" [Cellegummi slanger.pdf p.3].

Two rubber types dominate:

• NBR (Nitrile Butadiene Rubber) — the basis of the classic black Armaflex AF and Kaiflex KKplus. Good for indoor cooling installations at temperatures −50 °C to +110 °C.
• EPDM (Ethylene Propylene Diene Monomer) — the basis of HT variants. Withstands up to +150 °C, has better UV and ozone resistance, but a somewhat higher λ-value.

The decisive word is closed-cell. Each individual cell in the foam is closed and sealed, so water vapour cannot penetrate. This gives two advantages compared with open-cell mineral wool:

1. Built-in vapour barrier. The diffusion resistance µ is typically ≥ 10,000. By comparison, mineral wool has µ ≈ 1 (air). With 13 mm of elastomeric foam you get a vapour resistance equivalent to 130 m of still air. That is why no separate vapour barrier is required on cold pipes.
2. Moisture-stable thermal conductivity. If water penetrates mineral wool, λ can rise to double or more. Elastomeric foam does not absorb water to the same degree, so the λ-value stays stable over time.

The first commercial elastomeric foam was developed by Armstrong World Industries in the USA in 1954 under the name "Armaflex". It solved the number one problem on cold pipes: condensation. When Armacell was spun off from Armstrong in 2000, the Armaflex brand came with it. In the 1990s and 2000s, competitors such as Kaimann (Kaiflex), K-Flex and NMC arrived. Today, elastomeric foam is the Danish standard for indoor cooling pipes.

Originally the product was "mainly intended for cold installations, but as development gradually progressed, both sheet and tube materials are now also used for hot installations" [Cellegummi slanger.pdf p.4]. Rising oil prices have made cold loss more expensive: "It costs 10–12 times more to lower the temperature by 10 degrees than to raise it" [Cellegummi slanger.pdf p.4]. DS 452 (2011) now requires at least 29 mm of elastomeric foam on a 60 mm cooling pipe at 0/+22 °C, not 13 mm as before [Cellegummi slanger.pdf p.4].

The main constituents of the elastomeric-foam compound:

• Base polymer: NBR (nitrile rubber) or EPDM
• Vulcanising agents: Sulphur-based systems
• Blowing agents: Release gas during heat treatment and create the cell structure
• Flame retardants: Halogen compounds (chlorine, bromine) in standard products; halogen-free in NH variants
• Stabilisers and pigments: Carbon black gives the characteristic black colour
• Mineral additives: Zinc oxide (found in the SF990 datasheet as ≥1–5 % by weight) [Armaflex SF990 datasheet p.2]

Product families:

For ventilation and condensation insulation of ducts, sheets are also used in thicknesses from 6 to 50 mm, often self-adhesive.

λ-value as a function of temperature (AF/Armaflex): approx. 0.031 W/m·K at −20 °C; ≤ 0.033 at 0 °C (declared); approx. 0.036 at +25 °C; approx. 0.038 at +40 °C. λ rises with temperature, so for HVAC and cooling pipes (the core application) the low λ at low temperatures is a major advantage.

Vapour diffusion resistance: "The mu value, i.e. the ability to hold back vapour, is among the best, reaching all the way up to 10,000 mu" [Cellegummi slanger.pdf p.3]. Armacell improved µ from 7,000 to 10,000 via a smaller cell size in their BØG series ("Beregnet Øget Godstykkelse" — calculated increased wall thickness) [Cellegummi slanger.pdf p.4].

Mechanical strength: Tensile strength approx. 0.4 MPa, elongation at break > 100 %. Flexible, but cannot bear weight.

UV resistance: Low in the standard variant — must be painted or clad within 7 days for outdoor use [Cellegummi plader.pdf p.4]. EPDM and solar-collector-specific variants (Kaiflex Solar EPDMplus, Armaflex HT Solar) are UV-stable from the factory.

Chemical resistance: Good against acids, bases and most solvents. However, the adhesive does not bond to asphalt, bitumen or red lead [Cellegummi plader.pdf p.4]. For stainless steel pipes, the manufacturer must be contacted (chloride risk) [Cellegummi plader.pdf p.5].

• Tubes (pipe insulation, the main product): 2 m lengths, internal diameters 6–89 mm, thicknesses 6/9/13/19/25/32/50 mm. Standard (slit and glued) or self-adhesive (adhesive strip along the slit) [Cellegummi slanger.pdf p.7].
• Sheets (above Ø89 mm, where the tube stops): 1 × 2 m sheets, or rolls of typically 6 m². Thicknesses 3–50 mm. With/without self-adhesive backing. Thick sheets (32–50 mm) are used for ducts, vessels and large pipes.
• Tape (self-adhesive, 3 mm × 50 mm): seals joints. Must not be used as the sole fixing point — only as a supplement to gluing [Cellegummi plader.pdf p.4].
• Cord and square profile: gaskets and special jointing.
• Prefabricated fittings:
  • Armafix AF pipe supports — load-bearing PUR/PIR inserts surrounded by elastomeric foam, with built-in vapour barrier and self-adhesive aluminium shell [Cellegummi slanger.pdf p.23]
  • Prefabricated tees and bends for standard dimensions
  • Valve boxes (Dancap Valvbox is a popular Danish system)

• Indoor cooling pipes (standard, the classic use — district cooling, brine, glycol)
• HVAC / air conditioning — both pipes and ducts
• Heat pumps — refrigerant pipes and condensate lines
• Low-temperature installations down to −50 °C (cold rooms, freezer plants)
• Industrial cooling installations — process cooling, ammonia plants
• Marine installations — ships, where self-adhesive or halogen-free variants are preferred
• Food industry — due to the closed-cell structure, no fibres, hygiene-friendly surface
• Solar-collector installations — only with HT/EPDM variants
• Domestic water (BVK, BVV) — as thin insulation on small pipes where space is tight