The Type B-11 was adopted in 1944 as a winter flying suit to be worn as a set with the A-10 trousers. Until then, winter suits had been made of mouton, but the review of the cost, weight, and productivity of the suits resulted in the introduction of cotton B-9 and B-11. The hooded, cold-weather-insulating specification with a zipper and button front closure is inherited from the B-7 made of mouton. The B-9 had a quilted down lining, which was replaced with alpaca in the B-11. This was due to the fact that the jacket was made of the same material as the B-10 jacket for intermediate-zone use, which was adopted in the same year, with the aim of ensuring a stable supply. The cuffs of the B-9 were ribbed, but since it was assumed that the B-9 would be worn over the B-10 on missions to extremely cold regions, the ribbing was eliminated from the B-11, and an adjustable belt was added.