Humidity and temperature play an important role in the performance of cotton fibers in the testing laboratory. The fiber responds to these environmental conditions by seeking to establish moisture and temperature equilibrium with the surroundings. The time required to reach equilibrium moisture content varies according to the amount of moisture that moves into or out of the fiber sample. Important information can be gained from understanding this process which allows an intelligent decision as to whether the fiber should be tested or not. Preparation of the test specimen, work which produces heat, leaves the fiber in a continual state of transition attempting to reach equilibrium moisture content. Curves were developed relating the time to reach equilibrium moisture content from moisture contents outside of the acceptable ASTM conditioned range. If the amount of time to reach equilibrium from the fibers' present state is significant (> 500 sec), then the fiber should be further conditioned prior to testing or continued testing. The time to reach equilibrium can be reduced significantly by exposing the fiber to moving conditioned air.