Method and system for forming reinforcing fibers and reinforcing fibers having particulate protuberances directly attached to the surfaces

A method for forming reinforcing fibers having particulate protuberances physically and/or chemically attached directly to the surfaces of the fibers comprising converting a molten material comprising a material selected from a group consisting of glass, glassy material, ceramic material, carbonaceous material, metal, and polymeric material into fibers by extruding the molten material through orifices to form menisci, pulling a hot fiber from each meniscus through a region including an attenuation zone and a zone extending approximately 50 cm below the bottom of the menisci and contacting the hot fibers with a fluid having solid particles suspended therein while the hot fibers are in at least a portion of said region, wherein the particles adhere to the surfaces of the hot fibers and create protuberances thereon, the particles having a longest number average dimension within the range approximately 2 nanometers to approximately 30 micrometers.