gambeson

A gambeson (or aketon or padded jack) is a padded defensive jacket, worn as armour separately, or combined with  chain mail or plate armour. Gambeson were produced with a sewing technique called quilting. Usually constructed of linen or wool, the stuffing varied, and could be for example scrap cloth or horse hair. During the 14th century, illustrations usually show buttons or laces up the front.
See more at Wikipedia.org...

(n.)
Same as Gambison.
  

(An arming coat; see Aketon )

A kind of arming coat worn during the 13th - 15th century both as a complete armour unto itself and as padding for additional armour worn over the top. They were generally quilted, either sewn or stuffed with linen, tow or even grass. Most of the illustrations from the 14th century show many buttons or laces up the front, and there are a few examples that feature a high collar to assist in the defense of the neck . 14th century Aketons were generally cut wide around the arm holes in a manner that followed the line of the breastplate or cuirass . These extra-large arm-holes served to grant complete mobility for a full range of arm motion while providing a last-ditch defense of the area under the arm. I can find no evidence of Aketons ever being open under the arm, though this is a common SCA style. See also the pourpoint , a garment worn under the arming coat useful for attaching the laces for the attachment of a leg harness . A workable pattern for a 14th century model can be found in Chronique: The Journal of Chivalry #2 .
Major Developments during the 14th century
- 1300-1350 Knights wore the haubergeon over their aketon
- 1350-1400 Aketon shortened and begins to be worn under the jupon , sometimes the only body defense. Strongly wasp-waisted form common to the period.
- 1350-1400 Sleeves were sometimes "banana sleeved" or ballooning out or were narrow so as to fit under the arm harness . Both seem popular for the entire period.