Dry fly dressing gel - a classic. Gink is a light paste that turns to a liquid at skin temperature. Upon coming in contact with cold water it returns to a clear, unseen, invisible gel that keeps water from making your dry flies or streaking streamers, wet. Flies stay dry for the normal useful life of any and all dry flies astream.
Gink is easy to use. Simply dab a little Gink onto a dry, dry fly (before it is allowed to get wet) and rub it into the fly until dressed. Hackles do not become matted or caked.