Abstract: A calendering apparatus and method for heatsetting a traveling multi-filament tow basically utilizes plural heated rolls about which the tow travels in a sinuous path to be conductively heated by the rolls and, at each roll, a plurality of infrared lamps in an arcuate arrangement facing the portion of the respective roll in contact with the tow simultaneously applies infrared radiation to the opposite side of the tow. In one embodiment, this arrangement of infrared lamps is retrofitted to a conventional calendering apparatus. An alternative embodiment provides for reducing or eliminating the number of calender rolls followed by a series of infrared heating tunnels collectively effective to accomplish heatsetting of the tow. The speed and/or throughput rate of each calendering apparatus and method is effectively twice that of conventional equipment of similar size.