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 (fencing) or fastening a knob on the point ("blossom", French "fleuret"). In addition to practising, some fencers took away the protection and used the sharp foil for duels. German students took up that practice in academic fencing and developed the "Pariser" ("Parisian") thrusting small sword for the "Stoßmensur" ("thrusting mensur"). The target area for modern foil is said to come from a time when fencing was practised with limited safety equipment. Another factor in the target area is that foil rules are derived from a period when dueling to the death was the norm. Hence, the favoured target area is the