What is the best material to wear under FR clothing?

Best Materials to Wear Under FR Clothing for Optimal Protection

The simple answer to this is either FR clothing base layer garments, or for many the optimal undergarments for FR clothing are made using natural fibre such as bamboo, cotton, or wool.

Best Material to Wear Under FR Clothing

FR underlayer options are usually fire-resistant cotton blends; cotton treated with flame resistant chemicals, or a blend of cotton and modacrylic fibres. Modacrylic fibre has the benefit of giving inherent protection, modacrylic fibres such as Protal cannot melt, and give exceptional resistance to degradation under exposure to chemicals, abrasion or UV radiation. Of course, as undergarments many of these properties should not be particularly significant for most situations.

best material to wear under FR clothing


For comfort against the skin, and breathability to reduce bacteria build up, 100% cotton or wool, particularly Merino wool with its naturally occurring hypoallergenic properties, are often the best fabrics to wear beneath FR Clothing. Standard polyester, nylon, rayon and similar synthetic fabrics should always be avoided as although your FR outer garments are protecting you from flame, it doesn’t take a great deal of heat for these synthetic fabrics to start to melt which can, in the event of an accident, be worse than having no undergarments at all (melted fabric could be trapped between the skin of the wearer and the outer layer of FR garments).


Using the correct recommended materials under FR clothing is an extremely influential factor when mitigating Arc-flash risks. More than one layer of Arc rated FR clothing achieves higher protection against Arc-flash than the sum of the ratings of the individual layers. This is because of the gap between the garments giving an air space which provides additional thermal insulation. This is known as the benefits of layering. The only accurate way of getting an indication on how much extra protection can be achieved through layering with optimal undergarments is by Arc flash testing using the proposed garments.

Natural Fibres

Natural fibres tend to provide good wicking properties too, important considerations for the comfort of wearers, and whilst they will not be all be FR rated, have good inherent anti-static properties. If you need certification or a guarantee of performance it is important to use certified FR AS and if required ARC garments beneath your outer layers. It’s also worth making sure your garment sizing is correct to maximise the advantages of layering, particularly with ARC garments.

It’s vital when considering the best fabrics to wear beneath FR clothing that you consult with someone who understands the products you are considering, the potential risks that the wearer may be exposed to and ensures that all your garments work together effectively for the protection and comfort of the wearer.


It’s important not to overlook the comfort aspect; the danger of cutting corners here is the risk of wearers not wearing the correct undergarments and in so doing jeopardizing both their own safety and the compliance of their employer.

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