This group of fly tying materials includes delicate and colourful synthetic materials of varied structure. These are usually thin plastic films or bundles of multi-layer polypropylene fibres reflecting positive displacement, which makes them fit for constructing dry flies. Any shape and size artificial wings may be cut out of the single pieces of fly wing film. Fly wings are usually used in imitating the wings of Ephemera (mayflies), Trichoptera (sedge flies) or Plecoptera (stoneflies). Synthetic wings are also perfect for constructing nymph cases.