The production of very long glass nanofibers with lengths up to several centimeters was demonstrated using the Laser Spinning technique. It employs a laser to melt a small volume of a solid precursor material while a high-pressure gas jet drags the molten material away. Thus, the molten material forms glass fibers as result of its viscous elongation by the drag force and rapid cooling promoted by the gas jet. High quantities of nanofibers can be quickly produced with tailored chemical compositions. Previously reported analyses of the process revealed that the dimensions and temperature of the molten volume together with its viscosity to surface tension ratio are the main factors governing the formation of the nanofibers. Therefore, the influence of the working conditions on these parameters must be understood to control the efficiency of the process. In this work, we demonstrate that the surface tension of the melt can be controlled independently of its temperature, and consequently of its viscosity, by adjusting the relative humidity of the gas jet. This outcome increases the productivity of the process and expands its capability for the synthesis of glass nanofibers from fragile melts.