Troutline Biothread. We import this from Eastern Europe where it is used for tying nymphs and larva. This material is opaque when dry and becomes milky translucent when wet. It will be stiff out of the package, we recommend getting it wet before tying with it. Cut the section of material you want to work with and soak it in warm water for 3 to 5 minutes. The color will change from the opaque to milky transparent. Use different color threads for different effects on the end product. It is widely used by competition fly anglers in Europe. Length per bag is approximately 19″ Large is for hook size 8 and 10, medium for 12 and 14, small for 14 and 16 and x-small for 18-20. It is available in many colors.