A protective tube for insertion into a pipe or vessel containing a medium, a measuring apparatus having such protective tube and a method for manufacturing the protective tube are disclosed, the protective tube including a tubular member having a bore extending between an upper and lower end of the tubular member and having at least one helical fin on at least a section of an outer surface of the tubular member, winding around the outer surface of the tubular member and defining a flow channel along at least a part of the tubular member. At least one geometric parameter of the at least one helical fin is configured based on at least one process condition of the medium in the vessel or pipe.