Abstract A theory of flexibility of pipe bends perpendicular to the plane of the bend has been established. Experimental results are given in this paper verifying the derived bending equations. Results show the pipes to be more flexible than expected from the application of the “rod” theory. A flexibility factor is obtained which is identical with that found for the bending of pipe in the plane of its bend. The increased flexibility is caused by a distortion of the cross section of the pipe. There is no change in the torsional rigidity of the curved tube as compared with the rod theory. Transverse stresses similar to those caused by bending in the plane of the bend are set up in the pipe wall. Longitudinal stresses are concentrated at their point of maximum value and are of greater magnitude than expected from ordinary theory. The theory of bending of two-dimensional pipe systems in the plane of their bends is given additional experimental verification.