A process for the production of a yarn is disclosed, the process comprising providing a bundle comprising continuous filaments of a thermoplastic polymer, contacting the bundle with a sliver comprising fibers of a heat resistant material to form a mixed bundle, and applying a gas jet to the mixed bundle to distribute the fibers of the heat resistant material in the bundle. Also disclosed are yarns comprising filaments of a thermoplastic polymer and fibers of a heat resistant material, wherein the fibers are distributed between and among the filaments. Preferably, the heat resistant material is a non-thermoplastic polymer, especially an aramid. Yarns according to the invention find use in technical fabrics especially transmission belts.