A dielectric substrate comprises a resin composition impregnated with non-woven fibrous mat material having a thickness of 5 mils (127 micrometers), wherein the fibrous mat material comprises fibers, having a diameter of 1 nm to 10 μm, that have been extruded through one or more openings to produce fibers that have been collected in the form of a fibrous non-woven mat, and wherein the fibers exhibit a multi-directional orientation in the non-woven mat material. The dielectric substrate is useful in circuit materials, circuits, and multi-layer circuits, economical to make, and has excellent electrical and mechanical properties.