The aketon, gambeson, vambasium, and jack were military vestments, calculated for the defence of the body, differing little from each other, except in their names, their materials and construction were nearly the same, the authorities quoted in the notes, shew they were all composed of many folds of linen, stuffed with cotton, wool or hair, quilted, and commonly covered with leather, made of buck or doe skin.
Source: wiktionary