Thicker than transfer foils or leaf, embossing foil is metal sheeting that is thin enough to be easily manipulated or embossed with a stylus. Embossing foil comes in different thicknesses and colors. Too thick to crackle, its chief use with polymer clay is for faux cloisonné (with tinted liquid clay as "enamel") or as a backing for thin pieces of polymer clay (to provide extra stability or strength).
Depending on the technique you're attempting, you may be able to substitute regular aluminum foil or disposable aluminum baking trays for embossing foil.