A bulking process for glass fiber strands is provided which allows for increased bulking speed while reducing any decrease in the tensile strength of the bulked glass fiber strand yarn. The process involves conveying treated glass fibers having one or more water soluble, emulsifiable or dispersible thermoplastic materials having a melting or softening point of greater than around 100.degree. F. (37.degree. C.), one or more cationic lubricants and water to a heater to melt or soften the thermoplastic material present on the fibers, bulking the heated glass fiber strand, removing the bulked glass fiber strand at a rate less than the rate of conveyance to bulking, and collecting the bulked glass fiber strand yarn. The treated strand being conveyed to the heater can already be dried or can be wet. After removal from bulking, the glass fiber strand can be treated with a chemical treatment to assist in retarding any additional decrease in tensile strength of the bulked glass fiber strand. The heating of the treated strand can occur before or after the strand is conveyed at a faster rate to bulking than the rate of removal from bulking. The product of the process is a bulked glass fiber strand yarn having a reduced decrease in tensile strength due to bulking.