In Vacuum Infusion (VI) process, used to manufacture large composite structures, the fibrous preform undergoes large deformations during the impregnation due to the use of a flexible vacuum bag. Moreover, the resin pressure difference between the upstream and downstream sides of the preform leads to a non-uniform preform thickness during the mold filling process, which may degrade the part quality. Thus, the prediction of resin flow and preform thickness variations is a very important issue. However, fluid-structure interaction modeling is a difficult task, mainly due to the complex mechanical behavior of the preform. Indeed, the through-thickness deformation of fabrics depends on many factors such as loading type, fabric saturation and fabric type, and also on strain rate effects, as already observed in the literature. In this study, one focuses on the preform deformation during decompaction. Experimental measurements were performed using a universal testing machine with different strain rates, for two different types of fiberglass fabrics, i.e. a random mat and a twill weave fabric, in a dry or wet state saturated by liquids with different viscosities. From these fabric characterization tests, a constitutive model was deduced, which was subsequently implemented in a numerical software to simulate preform decompaction during VI process. Some VI process experiments were also conducted in order to measure the liquid pressure gradient and the preform thickness profile during the mold filling stage and validate the numerical results. It was found from fabric characterization tests that strain rate and viscosity have no significant impact on the preform response in decompaction, in the tested ranges of strain rate and viscosity, for both the random mat and twill weave fabric. However, the analysis of VI process experimental results highlights that, in the case of the twill weave fabric, a time lag appeared between the resin pressure rise and the preform thickness increase, which suggests that a viscoelastic behavior was nevertheless present; whereas in the case of the random mat, it seems thus sufficient to model the preform deformation occurring during the impregnation of VI process with a simple time-independent constitutive law.