With these threads from Gutermann Sulky it is easy to create attractive, unusual and astonishing visual effects. Glowy 40 thread glows in the dark. It works by the embroidery thread storing sunlight and UV light which then glows in the dark. The duration of the light exposure determines the intensity of the luminosity, so the longer the thread has been exposed to sunlight or UV light, the longer and brighter the colour will glow in the dark. Guaranteed for up to 50 wash cycles without reduction of the luminosity. Perfect for fine ornamental stitches, decorative seams and fun embroidery motifs.