Ballistic nylon is a thick, tough, synthetic nylon fabric used for a variety of applications. Ballistic nylon was originally developed by the DuPont corporation as a material for flak jackets to be worn by World War II airmen. The term ballistic nylon takes its name from the fact that it was intended to protect its wearers from flying debris and fragmentation caused by bullet or artillery shell impacts. It was not an effective defense against most pistol or rifle rounds (ballistic nylon has been replaced by Kevlar and other, more effective, bullet resistant fabrics for these cases) let alone the heavy 20mm and 30mm autocannons Axis fighters were often armed with.