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:

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:

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

Wool can be divided into three broad categories.

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

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:

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: