A theoretical discussion about the layer copper factor used in winding losses calculation

In one-dimensional analytical theories aimed at calculating winding losses in magnetic devices, one usually introduces a "layer copper factor" to take layer porosity into account. The existence of this factor has been accepted since 1966 although it leads to nonphysical equations. This paper is a short theoretical discussion explaining: 1) how the layer copper factor comes from neither a one-dimensional nor two-dimensional model; 2) the true meaning of this factor; and 3) how an erroneous justification has propagated since 1966 in scientific literature.