This article focuses on the evaluation of the water immersion properties of wood-plastic composite (WPC) made with industrial wood residues. The effects of fiber type and proportion on the dimensional stability of WPC were studied. The water absorption of WPC samples was studied using modeling techniques. Samples were prepared according to a process in two steps: (i) extrusion compounding and (ii) injection molding. The results showed that the water absorption and swelling varied with fiber source and increased proportionally with fiber proportion. The variations of the water absorption and swelling have been represented following the theoretical model of the Fick's law of diffusion. The parameters of this diffusion process such as diffusion and Fick's coefficients are subsequently identified and modeled by both numerical and experimental approaches. The novel modeling includes short term diffusion and long term diffusion parameters for a better representation of the complex sorption behavior of WPC.