This paper presents a continuum modelling framework for the processing for fiber composites. We consider a generic press forming process, in which a network of fiber bundles is deformed, infiltrated by a liquid resin and consolidated. The real system involves at least three or four constituents: solid fibers, liquid resin, void inside the fiber bundles and possible gas bubbles in the resin. We propose to describe this complex system by two continuum phases, one solid phase representing the fibers and their interstitial void, and one fluid phase representing the liquid resin and its gas bubbles. Based on the entropy inequality along with micromechanical considerations we establish in particular a constitutive relation for the intrinsic compressibility of the solid phase (i.e. the fiber bundles). The paper is concluded with a numerical example, focusing on the stress relaxation due wetting at purely volumetric deformation.