That's why the same grade of nylon seen in parachute harnesses is what he now uses for the shoulder strap, the one part of the bookbag most likely to fail. And for the grommets in the shoulder strap, he has switched from copper, which is relatively soft, to hard engineering plastics such as Delrin, which retain their shape and hold up nicely under loads of over 100 kilograms.
因此他將最易因載重而脫線斷裂的帆布背帶，改為與降落傘安全帶同級的尼龍帶；銜接背帶的扣環，也從較軟的銅環，換成堅硬不變形的塑鋼材質，即使長期承重上百公斤也不會損壞。