Sulky Premium Invisible Thread is a very fine .004 polyester monofilament that is soft enough for baby quilts or garments that will be worn next to the skin. It is much more heat tolerant than nylon; it will not melt with normal ironing through the cotton setting. It is perfect for machine "hand-look" quilting, stitching in the ditch, invisible appliqué, and hems. Choose smoke for darker fabrics and clear for lighter fabrics. Recommended Needle Size: 10/70 - 14/90