100% 100wt Filament silk from Japan. Great for machine and hand quilting when you want lots of stitching in a small space. It is very thin but, because it's silk, strong enough for machine quilting even on longarms! It is also great for applique because it is so thin, it just disappears into the fabric. It is favored by experts and not-yet-experts who want their applique to look like the expert's.