If possible, it is best if the asphalt is applied when the humidity is 50 percent or lower, especially when emulsions are used. With any type of asphalt a lower humidity is better. High humidity can cause an invisible film of moisture to collect on the roadway surface, which may interfere with the asphalt sticking properly to the surface. With emulsified asphalts, the emulsion will be slower to break in high humidity. With asphalt cement, which is shot at much higher temperatures than emulsions, steam can be seen rising as the hot asphalt hits the moisture on the roadway surface. As steam is trapped under the asphalt, small bubbles form and break as the air and moisture work their way to the asphalt surface.