Fabrication of layered thermoplastic polymer products involves applying heat and pressure to contacting thermoplastic surfaces and consolidating the interface. Polymer healing, referring to the intermolecular diffusion across the interfaces of thermoplastic tape layers in intimate contact, is one of the important steps responsible for the development of interlaminar bond strength and is strongly influenced by the temperature history. While the theory for healing under isothermal conditions is well established in the literature, the available descriptions of healing under nonisothermal processing conditions lack a sound fundamental basis. In this paper, a model for the healing process under nonisothermal conditions is developed starting from a fundamental formulation of the reptation of polymer chains. Considering the temperature dependence of the welding time, the bond strength is described as a function of temperature history. It is shown that, under certain nonisothermal conditions, considerable errors could be introduced in the prediction of the healing development using the models in the literature.