Whereas refining is required for the strength development of chemical pulps, it has been unclear how refining affects the utilization of the furnish strength, as reflected by the handsheet strength, in the machine-made paper (strength efficiency). This work examined effects of refining on formation and strength efficiency in twin-wire roll forming of never-dried unbleached softwood kraft pulp in a pilot machine investigation comprising three separate sections. The first section showed that a change in refining energy has no significant effect on formation, tensile strength efficiency, tensile stiffness efficiency, or compression strength efficiency at a given consistency when the fiber length remains similar. The second section demonstrated that a change in kappa number has no significant effect on formation or tensile strength efficiency at a given consistency when the fiber length of the refined pulp remains similar. Here, an increase in kappa number involved an increase in refining energy. The third section showed that a reduction in headbox consistency results in an improvement in formation and tensile strength efficiency that is similar in magnitude over the whole refining curve.