Projob Work Wear - FR Undergarments and FR Sock Technical


Projob logoThis section discusses the FR properties of the three principal fibres (Wool, Lenzing FR® and Kermel®) used in the construction of our Projob FR Undergarments and FR Sock, noting:

  • Projob FR Undergarments are constructed using a knitted blend of Wool (50%) and Lenzing FR® (FR Viscose) (50%)

  • The Projob FR Sock is constructed using a knitted blend of Kermel®, Lenzing FR®, Nylon and Lycra®.  

Wool, Lenzing FR® and Kermel® rank among the world's leading FR fibres. Fabrics manufactured from blends of these fibres provide protection from second and third-degree burns in applications where risk of exposure to flame, radiant heat, electric arc, flash fire and molten metal splash are daily realities. Lenzing FR® and Kermel® have been developed to fulfill the very high standards demanded of flame resistant work wear. When Wool and Lenzing FR® or Kermel® and Lenzing FR® are incorporated into a fabric's composition, the result is unparalleled protection and truly FR work wear. For example, ArcFlashWear's PR97® is a blend of Wool and Lenzing FR® woven as a Twill, while blends of Kermel® and Lenzing FR® woven as a Twill in ratios of 70/30 and 50/50 are known commercially as Kermel® V70 and Kermel® V50. These fabrics are used extensively around the world and are known for their softness, breathability, high tenacity and temperature resistance, inherent FR properties and for providing premium protection in multi-hazard environments. Kermel® V70 and Kermel® V50 are recognised as being two of the best performing station wear fabrics and are well supported and worn by fire brigades worldwide.

Flame resistance has a direct correlation to the Limiting Oxygen Index (LOI) of the fibre(s) used in a textile's composition. The Limiting Oxygen Index is a measurement, expressed as a percentage, of the minimum concentration of oxygen needed in air to support combustion of the fibre. Since atmospheric air contains an oxygen concentration of 20.95%, fibres with a greater value Limiting Oxygen Index can be considered non-flammable or flame resistant, although it is acknowledged that a Limiting Oxygen Index ≥ 26 provides for the safest level of protection.

The Limiting Oxygen Index of Wool, Lenzing FR® and Kermel® are:

  • Wool: 25 to 26

  • Lenzing FR®: 28

  • Kermel®: 32

  • Result: these fibres do not burn or melt like synthetics, which means human skin is much safer when next to these fibres.  

You can read more about the FR properties of Wool, Lenzing FR®, Kermel® and Kermel® and Lenzing FR® as a 50/50 blend, in the following sections.

Wool - The Natural Fibre 

woolWool is one of the oldest known natural fibres and is constantly in demand for its unique natural properties including comfort and inherent fire resistance, properties that science cannot yet replicate. The ability of Wool to absorb 30% of its weight in moisture vapour gives it superior comfort, insulation, anti-static properties and flame resistance. While Wool can absorb moisture, it also repels liquids. Wool has a natural elasticity greater than any other natural fibre, which makes it comfortable to wear as it fits the shape of the body.

Australian Merino is renowned for being soft and fine. Australian Merino is loved by producers and consumers for being a unique fibre that's easy on the skin and on the planet. Close to 80% of Australia's sheep flock is Merino, so the Wool produced is well suited to high quality apparel and top-end fashion houses. 

Wool is the remarkable result of millions of years of evolution, which has culminated in an array of unique and natural properties.

How Wool Protects

  • Soft and comfortable - because of, and in particular, Merino's exceptionally fine fibres, Wool is soft to the touch due to the fine quality of the fibre. Wool breathes with the body and keeps the skin dry and comfortable.

  • Elasticity - natural elasticity allows garments to stretch yet return to their original shape.

  • Breathable - Wool can absorb large quantities of moisture vapour then move it away to evaporate into the air, meaning Wool clothing is extremely breathable and less prone to clamminess. This process of absorbing and releasing moisture is known as 'hydrogen bonding' where the negatively charged oxygen atom in the water vapour molecule is attracted to the positively charged hydrogen atom in Wool's protein (keratin) backbone.

  • Warm and cool - Wool is an active fibre that reacts to changes in body temperature so it provides warmth when the weather is cold and aids cooling when the weather is hot. In hot humid conditions, Wool fibres remain cooler than the body. As a Wool garment touches the skin, heat is transferred to the garment, acting as a coolant. In cold climatic conditions, Wool fabrics actively generate heat through the 'heat of sorption' response. As Wool fibres absorb moisture they release stored molecular energy in the form of body-warming heat. As the fibre dries moisture is released, the energy is renewed and replaced.

  • Static resistance - because Wool can absorb moisture vapour, it tends not to create static electricity.

  • Easy to care for - machine washable, stain resistant, anti-wrinkle and odour resistant.

  • Reassuringly safe -  Wool is naturally flame resistant because it has a high ignition temperature (570° C to 600° C) and a high Limiting Oxygen Index (25 to 26), which means it is difficult to ignite: fire resistant (Wool does melt and stick to the skin and self-extinguishes when the source of flame is removed), is a natural barrier to UV and is healthy, by regulating body temperature and heart rate.

Wool can be divided into three broad categories.

  • Fine - the finest diameter Wool comes from Merino sheep. It is used for high quality, soft handling fabrics and knitting yarns and is highly valued by the world's leading fashion houses.

  • Medium - a wide range of Wools between fine and coarse is produced by crossing one breed of sheep with another. Many of these crosses have become established breeds, such as, Corriedale and are bred in large numbers. Medium Wool is used in a variety of woven apparel fabrics, knitting yarns and furnishings.

  • Coarse - many different sheep breeds produce coarser Wools and often are dual purpose breeds farmed with equal emphasis on meat and Wool. Romney produces long, medium-lustre Wool, which is particularly useful for carpets because of its strength and durability. 

Lenzing FR® (a Cellulosic Fibre)


Lenzing logo

Lenzing FR® is a special natural viscose fibre with unique thermal insulation and permanent flame resistance properties that help prevent heat stress and heat stroke. Produced from wood, a natural raw material, Lenzing FR® offers protection against heat and flame in a variety of different applications. Around the world, Lenzing FR® sets the standard for quality among cellulose fibres with an incorporated FR agent. Only Lenzing FR® is produced using the Lenzing Modal® process. This ensures that the very highest fibre tenacities are obtained and makes it possible to insert the FR agent in a permanent manner.

Lenzing FR® has a Limiting Oxygen Index of 28, which means that a minimum concentration of 28% oxygen would be required to maintain combustion of a Lenzing FR® sample when exposed to flame in a vertical plane. Since atmospheric air contains a concentration of 20.95% oxygen, any material with a greater value of Limiting Oxygen Index can be considered non-flammable or flame resistant. This property prevents combustion and therefore the propagation of fire to a wider environment.

How Lenzing FR® Protects

  • Permanent protection from heat - Lenzing FR® protects from all kinds of heat: fire, convective and radiant heat, electric arc flash, flash fire and molten metal splash. From a technical perspective, because Lenzing FR® is made of a natural raw material, it has a flame retardant substance incorporated throughout the cross section of the fibre. The protective substance cannot be removed by either washing or abrasion.

  • Fire - Lenzing FR® offers excellent protection from second and third-degree burns and goes one step further since its physiological properties reduce the risk of heat stress and heat stroke. In fire environments, Lenzing FR® offers premium protection against flame as:

    • Protection against second and third-degree burns.

    • Improves the performance and comfort of 100%  aramid garments.

    • Improves textile break-open characteristics.

    • Reduces the risk of heat stress and heat stroke. 

  • Radiant heat - radiant heat can produce severe burns and workers employed in casting industries or in proximity to a blast furnace are at particular risk. Lenzing FR® provides excellent protection from burns in all applications where radiant heat constitutes a risk. Lenzing FR®, as an insulation against extreme heat, offers:

    • Reduction of heat stress and heat stroke.

    • Optimum moisture management.

    • Performance remains in tact. 

  • Electric arc - injuries resulting from second and third-degree burns are common in electrical utilities and installations where electric arc flash is a major hazard. Electric arc flash is caused by ionised air and constitutes a major risk for workers. Molten metal splashes also pose a high risk since an electrical discharge can cause anodes and cathodes to melt or evaporate. Lenzing FR® protects against these risks by:

    • Providing protection in high voltage areas.

    • Offering a skin friendly textile.

    • Enhancing textile blends when used in conjunction with a selection of aramid fibres.  

  • Flash fire - in the petrochemical and law enforcement sectors, Lenzing FR® offers protection from heat produced by flash fires. The combination of protection and comfort is in high demand for these fields of work. The natural anti-static properties of Lenzing FR® lower the risk of static build-up. This in turn reduces the potential of initiating a flash fire due to static discharge. In flash fire environments, Lenzing FR offers:

    • Excellent anti-static properties.

    • Good breathability.

    • Is the perfect blend partner. 

  • Molten metal splash - in aluminium smelters, steel plants, casting plants and recycling installations, Lenzing FR® offers protection of a special kind. Workers in these industries can be exposed to dangerous levels of radiant heat and also require protection from molten metal splashes. Fabric such as ArcFlashWear's PR97™, which incorporates Lenzing FR® into its construction (together with Wool), offers protection from 800° C molten aluminium and 1400° C steel. Fabrics which incorporate Lenzing FR® into their construction offer:

    • Molten metal run-off (shedding).

    • Premium and advanced technical properties.

    • Optimum skin-sensory features. 

  • Lenzing FR® is the perfect blend partner - common Lenzing FR® blends include other high performance fibres such as:

    • Kermel®

    • Wool

    • Dupont™ Nomex®/Kevlar®

    • Teijin Conex®/Twaron®

    • Inspec Fibres/P84®

Kermel® (an Aramid Fibre)

kermel logo

Kermel® is a high technological polyamide-imide, 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. Kermel® is a smooth-surfaced fibre with an almost circular cross-section. This shape, as well as its modulus, makes it comfortable and very pleasant to the touch.

The fibre has a very high resistance to abrasion and a thermal conductivity, twice as low as any other aramid fibre. It also has an excellent resistance to chemicals. In addition, Kermel® is relatively strong against acid attacks, which makes it particularly useful in plants where acid splashing is a major hazard. When heated to very high temperatures, the fibre chars without melting or dripping, whilst retaining its structure and discharging very few fumes.

Kermel® Base Properties:

  • Thermostability - Kermel® fabrics are stable in flames and the integrity of the clothing is sufficient to enable the wearer to move away rapidly from the hazardous area. Kermel® fibre does not melt or burn when exposed to high temperatures. Exposure to such high temperatures will only make the polymer char slowly.

  • Non-flammability - Kermel® based garments are inherently and permanently non-flammable.

  • Thermal insulation - Kermel® fibre is an excellent thermal insulator, which allows good protection against heat, even with lightweight fabrics.

How Kermel® Protects


Fabrics and fabric blends, constructed from and with Kermel® fibre, are permanently non-flammable and give excellent thermal protection against flame and radiant heat. They give an effective answer to safety requirements by giving the wearer extra time to fight or escape from the hazard without suffering injury. Kermel® has a Limiting Oxygen Index of 32, which means that a minimum concentration of 32% oxygen would be required to maintain the combustion of a Kermel® sample when exposed to flame in a vertical plane. Since atmospheric air contains a concentration of 20.95% oxygen, any material with a greater Limiting Oxygen Index can be considered non-flammable or flame resistant. This property prevents combustion and therefore propagation of fire to a wider environment.

Kermel® fibre does not melt, nor form molten droplets and therefore will not stick to the skin. Instead, it will slowly carbonise. If Kermel® remains in a flame, it will blacken and become slightly rigid without shrinking or forming droplets. The textile structure loses its mechanical properties but maintains its structure, which is an essential point for use in FR protective work wear. These characteristics allow Kermel® to ensure a high level of protection, even after exposure to an intense heat flux. Kermel® fibre maintains maximum short term protection against very high temperatures of up to 1000° C.

Kermel® maintains its mechanical characteristics well beyond the melting point of most synthetic fibres. It is necessary to reach a very high temperature to notice a complete degradation of the fibre. At 400° C, only a 5% loss of weight can be registered with a thermogravimetric analysis at 5° C per minute.

Resistance to Chemicals and Acids

The chemical properties of Kermel® provide efficient protection against most chemical agents. Kermel® gives good resistance to cold acids, even when concentrated and dilute alkalis at ambient temperature, when immersed for extended periods. Kermel® also withstands most organic solvents, chlorine bleach, detergents and water vapour. For short period contact, that is, accidental contact such as splashes or projections, Kermel® retains its integrity and therefore maintains the protective screen effect.

After more than four days immersed in sulphuric acid, sodium hydroxide or acetone, Kermel® fibre retains more than 50% of its initial properties, which are unchanged in boiling water and steam.

These characteristics make Kermel® the fibre of choice in plants where chemical and acid splash risks are important considerations.

Kermel® 50% and Lenzing FR® 50% Blend (Kermel® V50)

Kermel® and Lenzing FR® fibre blended in a 50/50 ratio, known commercially as Kermel® V50, makes possible the manufacture of truly FR work wear. Kermel® V50 is specifically designed to provide unparalleled protection against the risk and hazards associated with electric arc and extreme heat. The blend is inherently non-flammable and its high level of performance against heat and flame will last for the lifetime of the garment. When exposed to very high temperatures and flame, Kermel® V50 carbonises and thickens. This process increases the protective barrier between the heat source and the skin. Both the Kermel® and Lenzing FR® fibres are stable under high heat conditions and will not drip, melt or burn like ordinary synthetic uniform fabrics containing polyester or nylon. Under very high temperatures Kermel® V50 fabric maintains its mechanical characteristics.

The blend is anti-static (to prevent ignition due to sparks) and since Kermel® is doped-dyed there is no carrier used to dye the fabric (carriers are highly flammable and can persist as a residue on the fabric). The blend is durable (to last about three times longer than an FR treated garment) and easy to maintain. As Kermel® is doped-dyed and non-pilling (the only aramid fibre to have this characteristic) it results in garments with exceptional durable aesthetics. Test results indicate that Kermel® when blended with Lenzing FR® is perfectly adapted to the requirements of end users for FR work wear. Kermel® and Lenzing FR® are the perfect blend partners and together offer:

  • A cost effective way of improving the comfort and performance of FR work wear. In addition, the blend optimises dye affinity, fastness to light and is naturally anti-static. As a result, Kermel® and Lenzing FR® blended fabrics are the real high performers among flame resistant fabrics. All over the world, Lenzing FR® based fabrics have achieved the optimum balance of properties in protective apparel.

  • Kermel® and Lenzing FR® protective work wear satisfies all requirements of the wearer in terms of safety and durability as well as comfort. The water vapour penetration of a Kermel® and Lenzing FR® blend is significantly higher than a 100% aramid fibre (that is, with both fabrics being of same weight and construction).

  • Protection - inherent round-the-clock protection, not just against heat, electric arc, flash fire and molten metal splash but also against many acids and chemicals. Both fibres will not melt or form molten droplets.

  • Non-flammable - with both fibres having exceptionally high Limiting Oxygen Indexes, the blend itself is inherently non-flammable.

  • Thermosatble - protective fabrics manufactured from the blend remain physically intact upon flame exposure with no hole or break-open.

  • The 50/50 2 x 1 Twill blend of Kermel® and Lenzing FR® is ideally suited for hot climates as the blend offers a high degree of comfort thanks to the flexibility and softness of the mixture. The blend provides constant protection from fire and heat flash hazards and also acid and chemical projections.