Yarn for reinforcing composite materials

A method for manufacturing a composite material, said method comprising forming carbon nanotubes, spinning said carbon nanotubes into a yarn comprising four strands of carbon nanotube fibers, treating said yarn with a pre-treatment of a thermoplastic resin to promote swelling of the yarn, wherein the pre-treatment is with at least one of the thermoplastic resins selected from the group consisting of PEEK, PEI, urethane or polyimide, passing said yarn through a plurality of layers having interstitial spaces filled with a resinous matrix, swelling the yarn and allowing the pre-treatment thermoplastic resin to fuse with the resinous matrix.