Because of its design, the MA-15 has been the most popular in the military and then in civilian life. Initially, the Womens Top Gun B-15 Flight Jacket With Patches was entirely made of nylon, both the lining and the outer. Both layers were lined with wool to keep the wearer warm. After a few years, the wool filling was replaced with polyester fibre filling. The wool filling was replaced with polyester filling because it is much lighter in weight, making the jacket lighter and providing more warmth.