Fig. 2 shows an example of sterile and viral filter barriers around a bioreactor. Describe the characteristics of each filter type; pre-filter for gases, sterilizing filter for gases, pre-filter media for culture media and solution, sterilizing filter for culture media and solutions and viral filter for culture media. Dotted lines indicate an alternative flowpath. The size of the filter cartridges is not drawn to scale and their location is only approximate. For clarity, only the main culture medium, one supplement and one pH-control solution are represented. Bag for supple ment solution Bag for control solution Overlay gassing Air o, N co, Sparging Off-gases Bioreactor Media preparation tank Media hold tank 0881 Pre-filter for gases Sterilizing filter for gases Pre-filter for culture media and solutions Sterilizing filter for culture media and solutions Viral filter for culture media Fig. 2