In one example in accordance with the present disclosure, a post processing system is described. The post processing system includes a cooling system to cool the polymer object and a heating device to raise the temperature of the polymer object. The post processing system also includes a controller. The controller determines parameters for heating and cooling. The controller also controls operation of the cooling system to pre-cool the polymer object and controls operation of the heating device to raise the temperature of the polymer object such that a surface of the polymer object rises above the melting temperature of the polymer while an interior portion of the polymer object remains below the melting temperature of the polymer.