Fireproof underwear is sized on your body, the same measurements as a suit, because it has to sit close to the skin to do anything at all. It is also the layer that decides whether the suit over the top of it still fits.
The quickest way to get it right
Size it from your suitUnderwear letters follow the same body ladder as suits at every brand here. If you are a Sparco 52 suit you are a Sparco M top and bottoms. If you have not bought the suit yet, measure your chest and waist first and use those, because the underwear goes on underneath and the suit has to be measured over it.
AChestAround the fullest part, under the armpits, tape horizontal.
BWaistAround your natural waist, level with the navel.
CHeightAgainst a wall with no shoes. Walero size on height as much as chest.
DHeadAround the widest part, above the eyebrows. Only needed for a two size balaclava.
Watch out for paired sizes
Most mid range tops and long johns are not sold in single sizes. They come as XS-S, M-L and XL-XXL, which means there are only three garments in the whole range and each one has to stretch across two suit sizes. The OMP Tecnica Evo, the Sparco RW-7 and the Alpinestars ZX Evo V3 all work this way.
That is fine if you sit in the middle of a band. If you are on a boundary, a range sold in single sizes will fit you better than the paired one. The Sparco RW-11 Evo runs XS through to XXXL as seven separate sizes, and the Alpinestars Race V3 runs S to XXL. Worth the difference if you are hard to fit.
Tops and bottoms by brand
SparcoLetters follow their suit ladder. XS to XXXL depending on the range.▼
Sparco publish no separate underwear chart. These are the bands from their own man body size chart, which is what their underwear letters follow.
AlpinestarsXS to XL published. XXL and 3XL are sold without published measurements.▼
From the size guide on the Race V3 Top Tech Layer. Two things to know. Their own chart jumps from 98 cm to 102 cm between M and L, so a 98 to 102 cm chest falls in a gap; ring us if that is you. And they sell XXL and 3XL without listing the measurements, so ring us for those as well rather than working them out from the XL row.
WaleroXS to XXXL. The only brand here that publishes garment lengths as well as body measurements.▼
Tops
Leggings and long johns
Walero size on height as much as chest, so read both columns. The XL and XXL height bands really are the same on their chart; the difference between those two is chest and waist, not length.
OMP and SabeltSold in letters with no published measurements.▼
OMP put a size chart on every suit, shoe and glove product page but not on their underwear, and Sabelt publish nothing for the UI-100. Rather than convert from another brand’s chart and get it wrong, size these from your OMP or Sabelt suit size, or send us your chest and waist and we will confirm before it ships.
Socks
Socks go by shoe size, not by clothing size, and the two brands that publish a ladder do not use the same one.
Alpinestars do not make an XS sock. OMP sell theirs in XS, S, M and L but only publish the shoe range for XS, which is UK 5 to 5.5. Walero sell XS, S/M and M/L. Nomex socks are noticeably thicker than everyday ones, so if you are buying boots at the same time, try them on together or allow for it.
Balaclavas
Most of the balaclavas we stock are one size and stretch to fit, including the whole Sparco RW-4, RW-7 and RW-10 range, the Alpinestars ZX Evo, the MOMO Pro and the Sparco Pista. Where a balaclava is sized, it is sold as two: Adult S/M and Adult L/XL. That covers the OMP One Evo and Tecnica Evo, the Alpinestars Race V3 and the Walero open face.
Open face and full face is a fit decision as much as a preference. An open face balaclava leaves the eye opening wide and suits a full face helmet with a wide aperture. A full face balaclava has a smaller eye slot and sits tighter across the nose. If you wear glasses, the open face is the easier one to get on without dragging the arms out of place.
Buying a suit at the same time?Order the underwear first, or at least measure in it. A two layer suit sized over a t-shirt and then worn over a Nomex top and long johns is the single most common reason a suit that should have fitted does not.
Not sure, or falling between paired sizes?Send us your chest, waist and height with the range you are looking at. Underwear is the one thing people order last and it is the one that changes how everything else fits. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Sparco bands from sparco-official.com. Alpinestars from the size guide on their Race V3 Top Tech Layer. Walero from walero.uk. Sock ladders from the size options on the products themselves. All checked 2 August 2026. OMP and Sabelt publish no underwear measurements at all, which is why they are not tabulated above.
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