I thought that silk noil was made from cocoons where the worms are allowed to transform into moths escape. The threads break when the moth emerges, making shorter threads. The resulting cloth has an interesting texture and still has the natural gum on it, making it more difficult to dye or to get the detail I like. Still, Boachu and the Hundred Family Coat, one of my favorites from my last series of paintings, is done on silk noil.
Looking into this a bit more, it seems that there is no guarantee the cocoons used in silk noil were the ones left behind when the moth escaped. They may have been damaged some other way. But they are not boiled, so I think it is safe to assume the silk worms were not killed.