A radar level gauge including a wave guiding structure and a cavity formed inside the wave guiding structure, and a dielectric filling member arranged at least partly within said cavity. The dielectric filling member includes a main body formed of a polymer material, at least one microwave absorbing element formed of a modified polymer material providing a microwave attenuation of at least 1 dB/centimeter at an operating frequency of the radar level gauge, the modified polymer material being obtained by modifying said polymer material with a filler material, wherein the at least one microwave absorbing element is integrally formed with said main body by sintering.