An improved heat transfer tube, an improved method of formation and an improved use of such a heat transfer tube is disclosed. The heat transfer tube includes an outer surface with a plurality of radially outwardly extending helical fins, the fins being grooved to define notches, a plurality of channels extending between adjacent fins, at least one nucleate boiling pore formed at the intersection of a notch and a channel. The fins are flattened or pushed down to form a primary nucleate boiling cavity within the at least one nucleate boiling pore; and the tips of the fins are further bent over or flattened to form a secondary nucleate boiling cavity within the at least one nucleate boiling pore. Also disclosed are improved refrigerant evaporator including at least one such boiling tube and a method of making such a boiling tube.