Per Brandin on Quadrates
I believed four strip rods would be more powerful than conventional six strip rods of the same length and weight. The difference in power between a four strip and a six strip rod is more subtle than it is dramatic, however, and the actual action and power of the rod is affected much more by the taper and by hollowbuilding than by choice of cross sectional design.
In a nutshell, the slightly greater power of the square section comes from the larger flats, which although slightly closer to the neutral axis of bending than on the six strip, are almost twice as wide (given equal volume of material). These wide flats also incorporate the densest power fibers of the cane. The engineers whom I understand to have figured this out (in theory at least) have come up with a stiffness factor of .812 for the square section and of .791 for the hexagonal section and a maximum stress of 1.54 for the square as compared to 1.39 for the six strip. As I understand it these figures do not take into account the fact that bamboo is not a homogenous material. In fact, bamboo becomes much denser as the outside of the cane is approached. This makes the wide flats of the four strip rod, whch incorporate these fibers, of even more significance than if the material were of equal density throughout. Four strip rods seem to have a wider power band than a six strip rod, almost like the torque of a long stroke piston engine.
Contrary to popular belief, however, four strip rods require more work to make than a six strip, primarily due to the wider strips which must be worked with and the desirability of squaring the ferrule to fit the shape of the cane section. Finishing and wrapping guides is also more time consuming than on a six strip rod.
Although the four strip rod has certain advantages as outlined above, there is one type of rod in particular where the six strip design is more effective. If we want a long rod for a light line, such as an 8 1/2' rod for #5 line, or 8' for #3, where extreme light weight and delicacy are the desired qualities rather than power range, we can achieve this result more efficiently by using the same hollowbuilding methods I developed for my four strip rods on these six strip rods. The reason for this is that because of the geometry of the cross sections, I can remove a greater percentage of weight from the six strip rod than is possible with the square cross section. This is precisely what is required when making long rods for light lines. As a result of these insights, I am now building six strip rods again in a limited number of models.