Flexible food packaging is traditionally formed by heat seal welding bars. In this process, heat is usually applied on both sides of the polymer films. SEALESTER developed a new welding technique for polymer films that relies on asymmetric heating. The films are placed on a silicone support maintained at room temperature, while a heated cylinder tool applies a pressure for a specified amount of time. As the film is heated on one side only, the evolution of the interface temperature with time depends on the relative thickness and different thermophysical properties of the three materials involved: tool, film and support. Heat sealing in polymers is a diffusion phenomenon which depends on contact time and interface temperature. This article presents the results of T-peel tests of specimens sealed on the SEALESTER machine. Two PET- PE films with different thicknesses of PE layers were investigated. The same fracture modes as for symmetric heating were found. Peeling forces at a deformation of 5% were determined for each sample. Results show that this force depends on the tool temperature and the sealing time. It increases with the increase of tool temperature or the sealing time until it reaches a maximum value. The evolution of the force corresponds to a peeling fracture mode. An Arrhenius time-temperature law allows predicting the value of this force. As for the constant value of the tensile force, it corresponds to a tearing + pealing fracture. It depends also on the peeling velocity of the machine.