The invention relates to a method for irradiating partly formed packages (10) with electron beam irradiation from at least one electron beam sterilizing device (18), characterized in that it comprises: providing at least one partly formed package (10) to be irradiated in a gaseous environment, and exposing the gaseous environment to a pre-determined pressure regulation cycle and exposing the partly formed package (10) to irradiation at least during a portion of said pressure regulation cycle. The invention also relates to a device for realizing said method. The invention further relates irradiation of a packaging material web.
