Abstract: For use in medical trays the filtering flat material (2) has to be such that no micro-organisms can penetrate through it. In order to arrange such a filter (1) for achieving closure of a tray's partial surface including through openings which ensures sterility, a closed sealing line, which surrounds the through openings, is formed in the area of each flat partial surface having through openings, along which two tray parts to be assembled and including co-operating clamping surfaces enable clamping the seal (3) of the filter (1). By the elasticity of the seal (3) sufficiently good closure is ensured even by small clamping pressure and even with not precisely plane clamping surfaces. The bond of the seal (3) to the filtering flat material (2) has the additional advantage that the filter (1) can also be arranged at a lower surface by pressing its seal (3) into a corresponding groove and does not loosen due to gravity.