Low add-on technologies have attracted more and more attention due to the shortage of water resources. In order to explore the mechanism of low add-on technologies, the states of water and the pore properties (pore size distribution, total pore volume, specific surface area, and the average of pore radius) of cotton fibers were investigated over a wide moisture range by using differential scanning calorimetry (DSC) based on the Gibbs-Thomson effect. A simple model of cotton fiber with various moisture ratios was given. Larger pores changed in size with the change of moisture ratio prior to smaller pores in both wetting and drying of cotton fibers. The information obtained could be used to explain the results of dyeing processes. Low add-on technology (wet pick-up 30-40%) was a favorable choice for surface treatment. Excellent surface performance of fabric could be obtained, and large amounts of water and energy could be saved by low add-on technology.