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Selecting the Most Appropriate FR Fabric and/or Fibre

Selection of the 'perfect' FR fabric and/or fibre is a complex process. Each FR fabric or fibre has particular properties which either provides benefits or shortcomings. Fabric manufacturers blend fibres in an attempt to balance these individual properties to maximise fabric performance. It is important that Corporations be aware of each fibre’s properties to ensure that garments selected meet the specific requirements of a given application.

When reviewing fabrics and fibres, Corporations should consider thermal protection, static resistance, comfort, durability, stability, employee acceptance and appearance, ease of care and maintenance, colour availability and initial and ongoing cost. There also needs to be recognition of special hazards such as electric arc, flash fire and molten metal and chemical splash. These particular hazards may require additional evaluation and/or PPC program investment to ensure employees are provided with the correct and hopefully 'perfect' protection.

Corporations should follow three basic steps when undertaking proper evaluation of different FR fabric types. They are;

  1. Identify the potential hazard - different hazards have different characteristics, which is why test results do not directly correlate to each other. Test results for electric arc flash should not be substituted for test results for flash fire.

  2. Identify industry consensus standards for the exposure - for example, NFPA 70E and ASTM F1959 and F1506 have been developed for electric arc flash environments while NFPA 2112 and ASTM F1930 have been developed for flash fire environments.

  3. Ensure testing has been conducted at independent laboratories - this will ensure that scientifically valid data is being assessed. There is no substitute for information generated at an independent laboratory. The leading independent testing laboratories for electric arc flash performance are Kinectrics and KEMA Powertest and for flash fire performance, the University of Alberta.

About Aramid Fibres

Aramid fibres (meta-aramid and para-aramid) are man-made high-performance fibres with molecules characterised by relatively rigid polymer chains. These molecules are linked by strong hydrogen bonds that transfer mechanical stress very efficiently, making it possible to use chains of relatively low molecular weight. The term aramid is short for 'aromatic polyamide'. Aromatic polyamides were first applied commercially as meta-aramid fibres in the 1960s, with para-aramid fibres being developed in the 1960s and 1970s. The first commercial aromatic polyamide was produced by DuPont™ and branded Nomex®. Thanks to its strength and heat resistance combined with tactile characteristics that were close to normal textiles, Nomex® was quickly adopted for a number of uses including protective apparel, insulation and more.

In addition to Nomex®, other world leading brands of aramid fibres include DuPont™ Kevlar®, Kermel®, Teijinconex®, Twaron® and Technora®. 

Aramid fibres are renowned for their high tensile strength. Aside from their resistance to abrasion and piercing, they also have high resistance to organic solvents and fire. They have no melting point and only begin to degrade at extremely high temperatures. They also have low flammability.

  • Nomex® starts to decompose at around 350° C. While not being as strong as Kevlar® and para-aramid variants, Nomex® has excellent thermal, chemical and radiation resistance that makes it a popular fibre for protective firefighter apparel and hazardous material clothing.

  • Kevlar® has outstanding strength-to-weight properties and an extremely high tolerance to heat that has made it one of the most popular aramid fibres for bulletproof vests. Kevlar® and other para-aramids do not degrade until above 500° C. These fibres also operate well in freezing temperatures and are nonconductive. 

  • Kermel® is a high technological aromatic polyamide, classified in the meta-aramid family. It is naturally non-flammable, which is a permanent characteristic thanks to its chemical structure including a high proportion of aromatic structures and combined double bonds. The fibre has a very high resistance to abrasion and a thermal conductivity twice as low as any other aramid fibre. It has excellent resistance to chemicals and acid attacks. When heated to very high temperatures, the fibre chars without melting or dripping, whilst retaining its structure and discharging very few fumes.

  • Tejinconex® is a high-performance aromatic polyamide fibre with excellent flame-proofing and heat resistance properties. Teijinconex® will not combust through exposure to direct flame or heat and it neither burns or melts, which means it cannot stick to human skin. It is an excellent thermal insulator and has outstanding chemical resistance. The fibre begins to decompose and carbonise at 400° C

  • Twaron® is a high-performance fibre and Teijin Aramid's flagship para-aramid product. It offers a unique combination of mechanical properties, chemical resistance, excellent durability and thermal stability. It is highly valued across a wide range of industries for the benefits it brings to a great many high-performance applications.

  • Technora® is a para-aramid fibre made from co-polymers. It was independently developed by Teijin and has been commercially available since 1987. Technora® has a range of unmatched performance properties: high tensile strength - weight for weight Technora® is eight times stronger than steel; good fatigue resistance; long-term dimensional stability; excellent resistance to corrosion, heat, chemicals and saltwater.

Aramid fibres share some general characteristics that distinguish them from other synthetic fibres, namely:

  • High strength.

  • Good resistance to abrasion.

  • Resistance to absorption.

  • Resistance to organic solvents and good chemical resistance.

  • No conductivity.

  • Low flammability with a high Limiting Oxygen Index (LOI) - Nomex® and Kevlar® 30, Kermel® 32, Teijinconex® 30, Twaron® 29 and Technora® 25.

  • No melting point.

  • Superior fabric integrity at elevated temperatures. 

  • Good cut resistance.

These unique characteristics derive from the combination of having stiff polymer molecules with strong crystal orientation as well as close interaction between the polymer chains due to the hydrogen bonds. The hydrogen bonds are aligned, for the most part, along the fibre axis, which gives them remarkable strength and flexibility.

When considering PPE for military, fire departments or the police, their personnel require the highest levels of protection, as well as comfort and wearability. They need superior thermal protection and flame resistance and resistance to tears and abrasions. What's more, they want comfort that comes with lighter weight materials, greater flexibility and increased breathability. Firefighter turnout gear made from aramid fibres meet ever-more stringent requirements in terms of protection, thermal insulation and wearing comfort. The wearer is not only protected against heat and flame, but also against hazards associated with electric arc and flash fire.

Police and Special Forces also face increasingly threatening or violent situations. Aramid fibres provide protection, not only against heat and flame but also against bullets, slashing and stabbing.

In short, aramid fibres provide the key benefits of inherent flame resistance, superior heat insulation, dimensional stability, no burning, melting or adherence to human skin and are strong, light, durable and comfortable.  

Key Determinants for Blended Fabrics

  • A blend is a fabric or yarn made up of more than one type of fibre. Blending is the combining or mixing of different fibres to achieve a desired characteristic. Blending can influence performance, colouring, strength, softness, moisture absorbency, ease of washing, resistance to wrinkling, ease of spinning and cost.

  • Blending achieves - 

    • Improvement in the quality of a fabric for meeting specific end use requirements such as performance, comfort or ease of care that would not otherwise be available in single fibres.

    • Improvement in the texture, hand or feel and appearance of the fabric.

  • When assessing PPC programs there must be a clear understanding of each fibre's characteristics, properties, advantages and disadvantages.

  • The traditional methods of manufacturing fabrics are weaving, knitting and braiding. Nonwoven fabrics are made by bonding or interlocking fibres or filaments by mechanical, thermal, chemical or solvent means. 

  • The individual yet combined properties of the blend and finished weight of the fabric will determine a specific end use, for example, the fabric’s ability to shed hot metal, the arc tested ATPV rating, the level of flash fire compliance and other types of protection, such as for welding and cutting and resistance to chemical splash/penetration.

  • Care programs must be instituted to ensure that optimum levels of protection are correctly maintained. Correct care procedures must be strictly adhered to since the thermal protective properties of any FR fabric can be compromised by the presence of contaminants on the fabric. Care and maintenance procedures should be based on the requirements of the fabric’s most sophisticated fibre.

To widen the specification of high-performance FR fabrics, principal or lead fibres such as Nomex®, FR Cotton, Kermel® and Kanecaron/Protex®, are often blended with one or a number of other high-performance fibres such as:

  • Anti-static - for electrostatic dissipation.

  • Aramid - for increased strength.

  • Kevlar® - for increased reinforcement.

  • Lycra® - for shape retention and comfort.

  • Lyocell - for high absorbency and heat capacity and softness to hand.

  • Nylon - for increased abrasion resistance.

  • Viloft® - for additional thermal properties.

  • Viscose® - for uniformity in dyeing.

  • Wool - for increased durability.

Some of the world's leading and technically blended FR apparel fabrics, used in the construction of the ArcFlashWear premium range, include:

  • E. I. du Pont de Nemours and Company (USA) - Nomex® blends, Nomex® IIIA, Nomex® MHP and DuPont™ Omega™ FR Hi Vis.

  • Bruck Textiles (Australia) - PR97®.

  • Kermel® (France) - Kermel® V50 and Kermel® V70.

  • Kaneka Corporation (Japan) - Kanecaron Modacrylic/Protex®.

  • Polartec® LLC (USA) - Polartec® FR Fleeces.

  • Westex® by Milliken (USA) - UltraSoft®, UltraSoft® AC and UltraSoft® and TrueComfort™ knits.