Isacord's Texlight Glow in the Dark Thread is a washable embroidery thread that stores UV and artificial light to make your design glow in the dark. Use for extraordinary effects on sports or kids' designs, logos, or monograms. In the dark, this thread displays a green luminosity, whose intensity depends on the duration of exposure to light. We recommend reducing machine speed and thread tension when stitching with this thread. 100% Polyester, 800 meter spool, use MEDIUM heat when ironing this thread.