Gtermann sulky glowy 40 thread pack of 7 two ply 100 polyester embroidery thread that glows in the dark after exposure to bright light these threads start off as subtle fixed colours then when moved into the dark they glow to vibrant fluorescent colours the intensity of the glow is determined by the length of light exposure ideal for embroidery designs as they will create an impact can be washed up to 50 times at up to 30c without diminishing the glow iron on low recommended needle