Based on a US Army A-3 Mechanic's Cap, the OOAL Cap from Nanamica is constructed in a 6-panel structure with hidden elastic at the back for a flexible fit.

The cap's made from a cotton/wool blend chambray, made with hard-twist cotton warp and pure Australian combed wool weft.

With the quoted size range of 53–63cm, it's likely to fit most people's heads.