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Materials & Performance

Elastomer Materials

Materials:  Flexseal couplings are manufactured using a highly versatile EPDM rubber sleeve with stainless steel clamping bands. The sleeve is used to create an air and watertight seal on the pipe surface and the stainless steel clamping bands produce the compressive force that forms the seal. Stainless steel shear bands are used in some of the product range to resist lateral movement across the joint caused by ground settlement.

Elastomers:  An elastomer can be broadly defined as a natural or synthetic elastic material. The elastomer compounds used in our coupling sleeves meet the requirements of BS EN 681:1. This
is a requirement of the coupling manufacturing standards and ensures that the EPDM rubber compounds used meet specified physical performance criteria and as such the longevity and performance of the products is assured.

EPDM Rubber (Ethylene Propylene Diene Monomer)


  • A high performance synthetic rubber.
  • Ethylene Propylene Diene Monomer has excellent resistance to ozone, weathering and sunlight.
  • Excellent heat resistance and very good flexibility at low temperature.
  • EPDM generic temperature range is -50ºC/+150ºC.
  • Fernco states a continuous operation at 80ºC. Intermittent at 100ºC.
  • Has a good general chemical resistance and can be used above ground.
  • Inherently has good resistance to alkalis, acids and oxygenated solvents.
  • Superior resistance to water & steam.


  • EPDM has poor resistance to oil, gasoline and hydrocarbon solvents.


Due to its unique combination of physical properties, EPDM can be used in an unusually broad range of products. Aside from applications requiring resistance to oil and hydrocarbon solvents, there is scarcely an application in which EPDM is totally unsuitable.  Because of its excellent resistance to ozone, sunlight and severe weather conditions, EPDM is ideal for outdoor service.

SBR Rubber (Styrene Butadiene)

Styrene Butadiene (SBR) is occasionally used in the Flexseal Coupling range as an alternative to EPDM for products with an underground use only.


  • Styrene Butadiene has excellent impact strength: very good resilience, tensile strength, abrasion resistance and flexibility at low temperature.
  • SBR generic temperature range is -45ºC/+100ºC.


  • Styrene Butadiene is not as suitable for above ground applications and has a lower heat resistance.
  • Poor resistance to ozone and sunlight: very little resistance to mineral oil, oil, gasoline and hydrocarbon solvents.


SBR is much like natural rubber in most of its properties. The physical properties meet the requirements of EN681:1 and therefore this elastomer is a good alternative to EPDM but cannot be used above ground. Also the material does not have the same resistance to high temperature as EPDM.

NBR Rubber (Nitrile or Acrylonitrile Butadiene)

Nitrile or Acrylonitrile Butadiene (NBR) can be offered as an alternative material for instances when the drainage effluent is contaminated by hydrocarbons.


  • Very good resistance to oils, petrol, diesel and greases.
  • NBR generic temperature range is -30ºC/+100ºC.
  • Good resistance to alkalis and acids.

Poor resistance to ozone and sunlight.


The physical properties of the compound meet the requirements of EN 681:1 NBR is used in specific application for effluent contaminated with hydrocarbons, oils, fats and greases.  It should be noted that the nitrile compound is classed as medium grade and is therefore only suitable for drainage applications.

Environmental Resistance Properties

Oxidation Resistance G-E F-G F-G
Ozone Resistance E P P
Weathering Resistance E F F-G
Sunlight Resistance E F P-F
Water Resistance E G-E G-E
Flame Resistance P P P
Heat Resistance G-E F-G G
E = Excellent G = Good F = Fair P = Poor


Chemical Resistance Properties

Oil and Petrol P P G-E
Animal and Vegetable Oils G F G-E
Alcohols F-G G F-G
Alkalis G-E F G-E
Acids G F-G G
E = Excellent G = Good F = Fair P = Poor


Stainless Steel - Grade 1.4301 (304) and Grade 1.4401 (316)

The term stainless steel is applied to a range of iron based alloys which rely on their chromium content for resistance to corrosion. The stainless steels used with our Flexible Couplings are classed as Austenitic Stainless Steels. The term Austenitic steel refers to the microstructure of the steel caused by the alloying elements. The steels used in the Flexseal Couplings range have 17%-18% Chromium content and 8% -11% Nickel content and are in full compliance with the manufacturing standards of BS EN 295:4 and WIS 4-41-01. Such steels offer a good combination of corrosion resistance, formability and weldability.

Product is normally supplied with Grade 1.4301 (304) stainless steel. Grade 1.4401 (316) can be fitted where a higher resistance to corrosive elements is required. 

Watermark Certificate of Conformity

Click below certificates for PDF download:

SAI Global Certificate WMK22178_Exp February 2021

WM022225 WMK Certificate Expires April 2024

OMK22225 OMK Certificate Expires April 2024

OMK22225 Product Schedule