Best Buy For Your Buck: This is the size for you if this is your go to thread for machine appliqué and quilting. 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 Sulky 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.