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That means the signal is entirely in the tin layer, if one is present. Not a good thing, as tin is not a very good conductor. Tin has about seven times the resistance of copper). So anything at 1MHz or higher should not have a tin layer. It needs to be bare copper. That means video cable, digital audio cable, RF coax or Category data cables all need to be bare copper. No tinned copper.
The best conductors are silver, copper, gold and aluminum respectively. Cost, weight and ease of handling dictate using copper or aluminum as conductors in most industries. Also it is used in piping as it is unreactive with water.