A method of metal layer formation which can satisfactorily eliminate the
problems caused by plating solution infiltration and is sufficiently
effective in reducing the permittivity of an insulating layer; and a metal
foil-based layered product obtainable by the method. The method is for
forming a metal layer on a surface of a porous resin layer and includes: a
step in which a porous resin layer having a dense layer as a surface part
thereof is used as the porous resin layer and a thin metal film is formed
on the surface of the dense layer by a dry process; and a step in which a
metal film is formed on the surface of the thin metal film by plating.
