the invention relates to a process for manufacturing a sandwich panel comprising a step to bake a stacked structure provided with : a honeycomb body ; a film pre - impregnated with a first resin with a polymerisation temperature t 1 ; and a first stack of fibre layers pre - impregnated with a second resin with a polymerisation temperature t 2 greater than t 1 , the film being arranged between the first stack and the body . the baking step comprises a first phase designed to use the film , to create a rigid barrier providing a seal from the second resin by polymerisation of said first resin , followed by a second phase designed to produce the skin starting from the stack , by polymerisation of the second resin .