This work explores the potential of recycling carbon-fiber–reinforced epoxy com- posites, focusing on the fundamental transport phenomena governing the interaction between water and the polymeric matrix. An experimental campaign was conducted to investigate the water uptake behavior of a commercial epoxy resin (HexFlow® RTM6) under hydrothermal conditions at 100 °C, 150 °C, and 200 °C. Gravimetric measurements were analyzed using analytical solutions of Fick’s second law, both in one-dimensional and cylindrical geometries, to estimate the apparent diffusion coefficients. The results confirmed the thermally activated nature of diffusion: the diffusion coefficient increases signif- icantly with increasing temperature, especially in the jump from 150 to 200, where the increase corresponds to approximately one order of magnitude.