A process for annealing photovoltaic polymer encapsulation film (3), the film comprising polymer molecules substantially oriented along a machine direction, characterized in that the film is heated, supported on a support surface of support means (12), with heating means to a relaxation temperature to increase the isotropy of the polymer molecules such that the film is at least partly annealed, the support means (12) comprising a fluid (13) between the film (3) and the support surface.