Rotor blade of a wind turbine, wherein the rotor blade comprises - a leading edge section with a leading edge and a trailing edge section with a trailing edge, - a root section with a root and a tip section with a tip, - a shell with a suction side shell section and a pressure side shell section, wherein the shell extends to the tip of the rotor blade and wherein the outer surface of the shell defines the outer shape of the rotor blade and the inner surface of the shell defines a cavity of the rotor blade, - a lightning protection system with an internal down conductor extending from the root section of the rotor blade to the tip section of the rotor blade, wherein the internal down conductor is connectable at the root section to a grounding system of the remainder of the wind turbine and at the tip section to at least one tip lightning receptor which is positioned at the outer surface of the rotor blade, and - an electrically insulating tip unit, wherein the tip unit is arranged in the tip section of the rotor blade in the cavity of the rotor blade and wherein the tip unit encapsulates at least a part of the internal down conductor in the tip section of the rotor blade, wherein at least a part of the tip unit covers the entire area between a part of the suction side shell portion and a part of the pressure side shell portion, and wherein the connection between the tip unit and the suction side shell portion as well as the connection between the tip unit and the pressure side shell portion is a cast interface, respectively, wherein the tip unit comprises a tip part which covers the entire area between the leading edge and the trailing edge of the rotor blade, wherein the tip part is located at the outermost part of the cavity of the rotor blade. wherein the rotor blade comprises - a leading edge section with a leading edge and a trailing edge section with a trailing edge, - a root section with a root and a tip section with a tip, - a shell with a suction side shell section and a pressure side shell section, wherein the shell extends to the tip of the rotor blade and wherein the outer surface of the shell defines the outer shape of the rotor blade and the inner surface of the shell defines a cavity of the rotor blade, - a lightning protection system with an internal down conductor extending from the root section of the rotor blade to the tip section of the rotor blade, wherein the internal down conductor is connectable at the root section to a grounding system of the remainder of the wind turbine and at the tip section to at least one tip lightning receptor which is positioned at the outer surface of the rotor blade, and - an electrically insulating tip unit, wherein the tip unit is arranged in the tip section of the rotor blade in the cavity of the rotor blade and wherein the tip unit encapsulates at least a part of the internal down conductor in the tip section of the rotor blade, wherein at least a part of the tip unit covers the entire area between a part of the suction side shell portion and a part of the pressure side shell portion, and wherein - a leading edge section with a leading edge and a trailing edge section with a trailing edge, - a root section with a root and a tip section with a tip, - a shell with a suction side shell section and a pressure side shell section, wherein the shell extends to the tip of the rotor blade and wherein the outer surface of the shell defines the outer shape of the rotor blade and the inner surface of the shell defines a cavity of the rotor blade, - a lightning protection system with an internal down conductor extending from the root section of the rotor blade to the tip section of the rotor blade, wherein the internal down conductor is connectable at the root section to a grounding system of the remainder of the wind turbine and at the tip section to at least one tip lightning receptor which is positioned at the outer surface of the rotor blade, and - an electrically insulating tip unit, wherein the tip unit is arranged in the tip section of the rotor blade in the cavity of the rotor blade and wherein the tip unit encapsulates at least a part of the internal down conductor in the tip section of the rotor blade, wherein at least a part of the tip unit covers the entire area between a part of the suction side shell portion and a part of the pressure side shell portion, and wherein the connection between the tip unit and the suction side shell portion as well as the connection between the tip unit and the pressure side shell portion is a cast interface, respectively, wherein the tip unit comprises a tip part which covers the entire area between the leading edge and the trailing edge of the rotor blade, wherein the tip part is located at the outermost part of the cavity of the rotor blade.