There has been a great deal of discussion about quadrate rod configuration in the recent past. Many fishers seem to think that the "quad" fly rod is just a new fad, but four-sided construction was part of the bamboo, rod-making tradition even before the turn of the twentieth century.
  It was W.E. Edwards, however, who first popularized the quad in the 1940s, a tradition carried straight through to 2003 by the late Sam Carlson, and now by Sam's long-time protege, Dana Gray. Per Brandin, too, has become well known over the past twenty years or so for his excellent quadrate designs.
  quad vs. hex
Cross-Sections of Quad and Hex Construction
    Sadly, quads never found the market always enjoyed by hexagonal rods. No doubt, the reason for the quad's relative obscurity was a function of the added difficulties in four-strip construction, making the quad considerably more labor-intensive and less cost-effective for commercial manufacturers of fly rods.
  Over the past several years, however, quads have become popular once again, resurrected largely because of the burgeoning, cottage industry of part-time and amateur rod-makers. For builders such as myself, the additional problems of four-sided construction do not pose deterrents of the same magnitude felt by manufacturers, and many of us are now happy to offer quadrate counterparts to our hexagonal rods.
  Four-sided construction provides a different "feel" from the hexagonal fly rod, an action which many fly fishers have come to prefer. Because of the different flexing characteristics of a square versus a hexagonal shaft (read, "fly rod"), a quad taper is designed, proportionally, with somewhat less cross-sectional mass than its six-sided "counterpart," and in consequence, the quad also feels a bit lighter in weight.
  quad rod
Quadrate Rod Revealing Its Intrinsic Elegance
    Ironically, despite their finer proportions, quads are said to have a measure of "reserve power" not necessarily present in the six-sided rod. This condition seems to derive in part from a greater density of power fibers per square inch than is present in a hexagonal rod, in part from the fact that there are fewer glue lines and more "uninterrupted" bamboo, and in part from greater available resistance to stresses of compression/tension through the casting plane -- a result of each individual strip occupying the full width of the rod. While the quad seems to have a more delicate feel and an easier casting stroke, deciding upon the "superiority" of a quad over a hex rod depends a great deal upon one's individual casting rhythms, expertise and taste.  
    Perhaps the greatest benefit, however, is that the quad behaves as a highly accurate fishing instrument -- a characteristic attributed to the theory that a square beam (quadrate fly rod) wants to flex principally up and down across its "flats" (the casting-plane), just as it also wants to resist flexing across its wide corners. This tendency, of course, insures that the rod, line and leader will unload more precisely in the direction of the last, forward cast. Conversely, a hexagonal rod, with its less pronounced corners, is more "willing" to flex in any direction. Thus, any torque (or other imperfection) induced by one's casting stroke has greater potential in a hexagonal rod to translate into an inaccurate cast. So goes the theory, but again, much depends upon the caster's own technique of delivery.  
  quads vs hex  
    In the end, though theory seems to be on our side, it may be very difficult to prove with anything like scientific evidence that a quad will cast a line better than its hex counterpart. Nevertheless, even by the most conservative estimates, the quad is without question, equally good.  

    The primary objective in hollowing a fly rod is to reduce what's often referred to as "swing weight," a term used to describe the felt-effect of momentum and inertia in a fly rod when set in motion. It's the length of a rod and the distribution of mass (weight) down the shafts that are determining factors here, and the rod itself, without line and reel, are what we mean to consider.  
    Large bamboo rods, in particular, often begin to feel sluggish and clumsy when being cast, soon tiring one's wrist and shoulder. The fisher may seek to balance a large or heavy rod with a similarly large and heavy reel, but this quickly becomes a "lose-lose" proposition. Counterbalancing a heavy rod with a reel may seem fine when merely holding the outfit in one's hand. But upon casting, the whole rig remains "loggy," since all the weight (now, including the heavier reel) still needs to be set into motion.
  fluted strips
Properly Prepared Fluted Strips Ready for Gluing
    Mass, wherever it is located, is the real enemy, and the greater the reduction of weight down the shaft, beyond a caster's hand, the more "crisp" and responsive a rod will feel -- thus, less need for counterbalancing. This produces a "win-win" situation, as the entire outfit now will have become as light as possible.
  Not all fly rods will benefit significantly by being hollowed, but those built for five-weight lines (in lengths of seven-and-a-half feet and more) reach the point where hollowing can make a positive difference. For still larger rods, hollow construction will greatly improve the feel of a rod in the caster's hand, allowing the action of the taper to do its work while avoiding the deadening effect of unnecessary mass.
  fluted construction
Cross-Sectional Strength of Fluted Construction
    The first hollow-built fly rods came with Edwin C. Powell's patent back in 1933, but it was Lew Stoner of The Winston Rod Company who, shortly thereafter, devised a different hollowing method called "fluting." This technique differs significantly from Powell's basic hollowing in that each strip, instead of simply having its inner apex planed off, actually has a concave channel carved down its center line. Stoner's revolutionary technique immediately won notoriety and established several new world casting records.  
    One great advantage of the fluting method over other hollowing techniques is that one can "dig" deeper into the strips, removing weight at a still greater distance from the center of the glued section. And this becomes possible because the outer edges of each flute, rounding back toward the center-point as they do, will preserve a very broad gluing surface. Most of the stresses in a flexed rod are registered on or near the outer surfaces, so the wide glue-line of the fluted rod ensures structural integrity, while useless and detrimental weight in the center has been removed.
  A final advantage of hollow-fluting is that the flutes of a glued section actually form a set of "vaults" down the length, and as the Romans discovered, the vault is a very powerful architectural structure. Thus, the fluted shapes themselves lend a measure of resistance against forces of bending.