Poly yarn is also known as floating yarn and Poly wing material. Polypropylene yarn is slightly crinkly and can be cut to any length. It is useful for dubbing with furs and for winding on hooks for hopper bodies etc. The white is commonly used for upwing and spentwing flies as well as being a major wing material for streamer type flies. Use the fluorescent colours for tying strike indicators. Also the material to use for the 'Toad' fly pattern.