The manufacture and increasingly widespread use of thermosetting/thermoplastic pre-preg fabrics suggests that new finite strain material models are needed to describe their behaviour during forming. Determining the appropriate models to apply involves the correct description of the anisotropic visco-elastic behaviour of these materials and the development of methods for measuring the material properties. This paper addresses the former issue, by presenting a logical method for formulating the equations of state for an incompressible continuum reinforced with inextensible fibres. Utilising body tensor fields and the internal variable concept, various thermo-rheological constitutive models are derived, based on the free energy and the dissipation function, which arise naturally in the Clausius Duhem inequality. The inherent assumptions leading to the finite strain Maxwell and Kelvin-Voigt material models are discussed. The method outlined here is general, therefore it allows the formulation of constitutive equations with a clear understanding of the limitations embodied in the resulting models.