A filter insert for an air filter comprises a bellows (2) which is made from filter material that is folded in a zigzag-shaped manner. The bellows forms a plurality of adjacent pockets (5). First folds (3) are formed at the top of the pockets (5) between the pockets (5) of the folded filter material. A seal is provided on the bellows (2). In order to be able to adjust the bellows to any shape, the folded filter material has an additional folded structure that extends transverse to a longitudinal direction (L) of the pockets (5) such that second folds (4) are formed which extend substantially transverse to said longitudinal direction (L). The front and rear face (6, 7) of the bellows (2) are formed by cuts extending transverse to the longitudinal direction (L) of the pockets (5) in order to be able to cut the bellows (2) to size.