Abstract: Disclosed is an optical waveguide fiber coating system having means for cooling the hot fiber prior to the time that the fiber enters the coating apparatus. The cooling means comprises an elongated coolant tube through which the fiber passes. Cool dry helium is flowed into that end of the coolant tube into which the fiber enters. In a preferred embodiment, the coolant tube is surrounding by a chamber containing a liquified gas. The helium is cooled by flowing through a coil submerged in the liquified gas prior to being flowed into the tube. An iris diaphragm located at the fiber input end of the coolant tube prevents the entry of moist, warm air into that tube.