The RW-4 is Sparco’s FIA race sock, part 001516BI at £22. Built from two layers of soft-touch Nomex and approved to FIA 8856-2018.
Most FIA-regulated series that require approved gloves and underwear also ask for approved socks, and the RW-4 covers that requirement. The dual Nomex construction handles thermal and flame protection, while the soft-touch finish stays comfortable over long race stints. Rougher single-layer alternatives cause more irritation, and that matters if you are wearing them through a full championship day.
White only. Sizes XS through XL. These are a consumable; most drivers run two or three pairs in rotation and replace them when the fabric starts to thin.
If you are building a compliant FIA base layer kit alongside gloves and underwear, the RW-4 is the straightforward choice to complete it.
Do I actually need FIA underwear?
If your championship requires it, this is the layer scrutineers ask about, and it is strongly recommended under any suit regardless. These socks are homologated to FIA 8856-2018, the current FIA standard, so the label is there when scrutineers ask for it. Our guide on whether fireproof underwear is mandatory covers the rules championship by championship.
What size should I go for?
Sizes run from XS to XL. Underwear layers should sit close to the skin without pinching, as loose fabric wrinkles under the suit and gets uncomfortable fast. Between sizes, take the smaller one for a base layer.
How do I wash it?
Underwear layers are the one bit of racewear you should wash after every use: cool and gentle, no bleach or fabric softener, air dry. That keeps the suit itself needing far fewer washes. Full routine in our racewear care guide.
