The continuous phase transition during film blowing of low-density polyethylene from melt to semicrystalline solid is analyzed in this study. The rise of stresses in the melt is described with a multimode Phan Thien-Tanner model and compared with the results obtained with a multimode Giesekus model. The stresses of the shear flow in the annular gap of the extrusion die serve as a starting condition for the simulation model. The temperature drop is calculated taking into account the temperature profile within the film and the dependence of the material parameters on temperature and crystallinity. The selected form of the crystallization equation allows the precise fitting of the experimentally observed temperature plateau. A modified Hookean model is used for the stresses in the growing semicrystalline solid phase. The stresses in the solid phase increase and in the melt phase decrease during the affine deformation of the two phases. The results for temperature drop, radius growth, and velocity increase are in excellent agreement with experimental data. The deformation rates predicted with the Giesekus and the Phan Thien-Tanner model reveal a characteristic difference between both the models. (C) 2018 The Society of Rheology.