Birch Polypore,Razor strop fungus [Piptoporus Betulinus] Birch polypore is in the family Fomitopsidaceae and is known as a bracket fungus,a fungus which grows horizontally out of the side of the Birch tree. Birch Polypore Identification Birch polypores fruit exclusively on birch trees in semicircular or kidney-shaped forms. In-rolled caps range from white to tan, and from 1 to 10 inches in width It is also known as the razor strop fungus for good reason too as you can cut a strip from it and used it to strop your knife blade. Cut a piece of polypore to use as a strop. Stropping my blade using a piece of wood as a back board to give support. The clean white flesh has anti-bacterial qualities and can be used as a plaster. Make four slices the width and length you require your plaster, then slide the knife under the cut then lift the plaster away with your knife,make sure your knife is clean. When applying, stretch slightly and gently squeeze and the polypore will bind to itself. You can reinforce with cordage/grass/bark whatever you've got on you really.