A filter holding device (1; 41; 75; 81) arranged for providing at least one filter (7; 43a, 43b; 85) inside a flexible bag (3; 71), said filter holding device comprising attaching means (19a-d, 21a-d; 79; 83) for attaching the filter holding device to an inner surface of the flexible bag such that the at least one filter held by the filter holding device is provided at a distance from the inner surface of the flexible bag.