Sheet material especially useful for circuit boards

A process for the production of a sheet material, comprising, heating and applying pressure to a multilayer structure, comprising at least two outer layers of a nonwoven fabric of short high tensile modulus fibers and at least one inner layer containing a thermoplastic with low moisture absorption, said thermoplastic is disposed between said outer layers to produce said sheet material in which:

• at least a major portion of said thermoplastic polymer is bound to at least some of said of high tensile modulus fibers;
• and
• through a cross section of said sheet material, from the center of thickness of said sheet material to both of the surfaces of said sheet material, a concentration of said thermoplastic polymer relative to a concentration of high tensile modulus fibers, decreases;
• and
• impregnating and coating said sheet material with a thermoset resin and curing said thermoset resin.