Toner Reactive Foils are very thin pigments on 1/2mil Mylar carrier. The foil is heat-transferred on top of a toner image and then ironed on. Used in the etching process for making printed circuit boards, this foil performs two very important functions. First, when transferred on top of the toner it seals the image to prevent etchant from permeating into the granular nature of toner which would normally result in pitting of the base metal. Secondly, its plastic "top coat" gives the toner extreme rigidity allowing you to directly rub a sponge full of etchant right over the copper surface without damaging the toner image. For use with TTS-10 Toner Transfer System.