PURPOSE: To see that it is excellent in dielectric property and does not bring about exfoliation by constituting this out of an insulating layer wherein mixed unwoven fabric consisting of fluororesin fibers and glass fibers is used as base material and it is combined with low permittivity thermosetting resin the permittivity of the hardening matter of which is not more than the specified value at specific frequency.

CONSTITUTION: Fluororesin fibers consisting of polytetrafluoroethylene, tetrafluoroethylene, hexafluoropropylene copolymer, olefin-tetrafluoroethylene copolymer, etc., and glass fibers such as D-glass wherein the content of SiO2 is, for example, 50wt.% or more, S-glass, SII-glass, t-glass, quartz glass, etc., are mixed at specific rate and are made the base material of mixed unwoven fabric. And it is suitable that an insulating layer, wherein cyanate resin and thermosetting resin with low permittivity of 3.5 or less at 1MHz, wherein high boiling point compounds, wherein 2 to 7 pieces, on an average, of aromatics which are nonsubstituted or substituted for halogen atmos or low-grade alkyl groups are coupled in a straight chain shape, and arranged to the cyanate, are combined, should be used. A material for printed wiring can be obtained, which is excellent in dielectric property and in which shrinkage in laminate formation is small and which does not bring about exfoliation, etc.