This polyester embroidery floss appears white, but contains a photoluminescent pigment. Just a few minutes exposure natural or artificial light is sufficient to provide a sustained greenish-white glow--the longer the exposure, the longer the glow lasts! Non-toxic and washable, this thread is a great way to add an unexpected accent to embroidery projects, and other crafts, too. It has the same 6-strand structure as standard DMC mouliné, and can be easily combined with cotton or metallic floss colours.