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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.
Tin (Sn) was first used as an alloying element with copper to form bronze, which is much more easily castable than copper and enabled the creation of more complex castings. It is a soft metal with a shiny silver color, and is very corrosion resistant in air and water.