Sulky Premium Invisible thread is a very fine .004 monofilament that is soft enough for baby quilts or garments that will be worn next to the skin. Quilters prefer our polyester invisible thread instead of nylon because it has a more flexible, soft touch. It is much more heat tolerant than nylon; it will not melt with normal ironing through the cotton setting. Works well in the bobbin; also ideal on sergers. It does not fuzz, fray or shrink.