Tin foil hat radio with a metal bucket. The AM radio is completely inside a metal enclosure. This leads to a noticeable reduction in signal strength received by the AM radio. The efficiency of a metal enclosure in blocking electromagnetic radiation depends on the thickness of the foil, as dictated by the "skin depth" of the conductor for a particular wave frequency range of the radiation. For half-millimetre-thick aluminum foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked, although aluminum foil is not sold in this thickness, so numerous layers of foil would be required
Foil opal Foil opal Foil opals are simulated opal gemstones that first came into vogue during the jewelry-making boom of the late-Victorian era. Across Europe and the United States, these faux gemstones joined their paste counterparts (simulated diamonds, emeralds, rubies and sapphires made from glass) as the need for jewelry outstripped both gemstone availability and nouveau middle-class budgets. The term 'foil' refers to an actual metal foil that was sometimes used to create reflection and sparkle behind milky glass or quartz faces. Though technically incorrect, other simulated opals with various types of sparkling inclusions or shiny backings are sometimes also referred to