The non-isothermal flow during compression molding of thermoplastic-based composites having a planar, randomly oriented fiber structure has been investigated. Local interactions at the bundle-bundle level were measured and a constitutive equation was derived to describe the shear and squeeze flow of the composites. This equation contains only micro-mechanics-related variables, and accounts for the temperature dependence of the interaction forces. The flow of the material under industrial processing conditions can thus be related to the deformation mechanisms of the reinforcement structure at the scale of the individual fibers. Good agreement was obtained between the predicted and experimentally observed rheological behavior of the composites in both shear and squeeze flow. The use of this approach to analyze the industrial molding of complex-shaped parts is discussed.