Cellulose, the most abundant biopolymer in the world, is naturally available and can act as a starting material for various chemical modifications that enable it to take the place of fossil-based materials. Cellulose derivatives, synthesized through the modification of cellulose find their applications in different fields such as food, pharmaceuticals, barrier materials, paints and coatings, packaging etc. An obstacle that retards the widespread usage of cellulose derivatives in industrial applications is moisture and its effects. Cellulose derivatives can absorb moisture and certain cellulose derivatives such as hydroxypropyl cellulose dissolve in water. However, the amount of moisture absorbed from the surroundings by each material depends on the relative humidity to which it is exposed and more importantly, the chemical substituents present in the cellulose derivative. Furthermore, it has been suggested that absorbed moisture can cause the relaxation of polymer chains and increase the molecular mobility. Therefore, the focus of this study is to investigate the influence of chemical substituents and relative humidity on the moisture absorption, and the subsequent effect of moisture on the relaxation and molecular mobility of the polymer chains. This is accomplished by studying cellulose derivatives having different chemical substitutions such as cellulose acetate, ethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose, stored at various humidities. Dynamic vapor sorption measurements will be performed to analyse the water sorption of the materials and dynamic mechanical analysis will be carried out at different humidities to estimate the polymer chain mobilities. Further, chemical characterizations such as FTIR spectroscopy will be performed to get an idea on the chemical interactions in presence of moisture. This study will prove to provide a holistic understanding on the water interactions in the most prominently used cellulose derivatives.