The present invention relates to a level gauge system for determining a filling level of a product contained in a tank, comprising a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagating device connected to the transceiver and arranged to propagate a transmitted electromagnetic signal along a generally vertical path towards a surface of the product inside the tank, and to return a surface echo signal resulting from reflection of the transmitted electromagnetic signal at the surface of the product contained in the tank; and processing circuitry connected to the transceiver and configured to determine the filling level based on the surface echo signal. A surface of the signal propagating device comprises a surface portion that exhibits a wettability defined by a contact angle between the surface portion and water being less than 30°.