The performance of cellulosic materials is intimately linked to their moisture content. Over the last century, many studies have been devoted to examining the moisture uptake in equilibrium with surrounding environmental conditions. However, with the adoption of automated sorption balances in laboratories worldwide, it has become increasingly popular to study the approach to equilibrium, i.e., sorption kinetics. Recording the moisture content change between two equilibrium states produces a wealth of data, which necessitates a robust methodology for analysis. In this study, we employ exponential decay analysis on sorption kinetic data obtained in a previous study for loblolly pine, holocellulose, office paper and microcrystalline cellulose. Unlike other methods that are constrained by a fixed number of fitting parameters or similar constraints, exponential decay analysis is a flexible, data-driven methodology for analyzing sorption kinetics. No physical meaning is assigned to the output from the analysis. However, the methodology yields robust results in relation to various measurement uncertainties. As a result, exponential decay analysis can provide a reliable description of the dominant time scales of sorption kinetics. Hereby, the methodology offers a new way to evaluate the suitability of theoretical models for describing sorption kinetics.