A helicoidally finned tube for use mainly in heat exchangers. The tube comprises a cylindrical tubular member which carries or is integral with a helical member the turns of which form the fins of the tube. The fins are provided with ripples which extend from the outer rim of the fins inwardly and the depth of which diminishes toward the tube center. The ripples serve for diverting a cooling medium inwardly to hotter parts of the tube thereby improving its heat transfer performance. The helicoidal member has rippled sections alternately with level sections, the rippled sections subtending an angle not exceeding about 90 degrees and both types of sections on successive turns registering with one another in the direction of the axis of the tubular member. The spacing of the sections is substantially equal to a quarter of the circumference of the tubular member so that the rippled sections of the helicoidal member occupy diametrically opposed positions on the tubular member, the ripples being disposed generally transverse to the direction of airflow. The ripple-free sections, thus positioned, facilitate removal of impurities precipitated in the fin gaps (FIG. 9).