Thanks to Maggie Backman for this wonderful article on silk:
If silk thread were a person, it would be a supreme overachiever. It has properties valuable to anyone seeking perfection in sewing projects. It is strong and fine, flexible and durable, long-lasting and lint-free. Yet it has carried a slightly nefarious reputation as a sewing-machine thread. There are claims that it snags and breaks in machines, that garments made with it must be dry-cleaned, or that it can shear right through fabric, destroying seams. The truth is, with understanding of its origin, care, and how to match thread type to projects, silk thread is an unparalleled asset as a machine-sewing thread. I’ll explain the difference between the two types of silk thread, spun and filament. Then, I’ll focus on the extraordinary qualities of silk filament thread, which is a superior sewing machine thread when the correct twist and weight is selected for a project.