Filter unit for connectors comprising at least a substrate (2) made of electrically insulating material and having two mutually opposite sides and through openings (3) for contact elements of the connector, capacitors being situated at least one of the two sides of the substrate in the region of the through openings, which capacitors each comprise at least one first conducting layer (5) in contact with the substrate, a dielectric layer (7) and a second conducting layer (9) and there being provided above each of the capacitors a cover layer (13, 22) composed of at least one first flexible layer (13) substantially covering the top surface of each of the capacitors and having a low moisture absorption coefficient and a high moisture diffusion coefficient and a second hard layer (22) at least entirely covering the first flexible layer and having a high moisture absorption coefficient and a low moisture diffusion coefficient.