The double-wall version has become the preferred bat for many softball players. Technological advances and enhanced manufacturing materials have strengthened the bat's durability and boosted its overall effectiveness. "The intent of this design is to intensify the 'trampoline effect,'" states Softball Bats. "Independent testing has proven double-wall bats provide an edge in performance." Adds Epinion.com: "Double-walled bats are a variation on the trampoline effect."
History
According to "Softball Magazine," by the late 1980s, softball slugger Ray DeMarini had become convinced that "factory bats were far superior to those available to the general public." In 1989, he founded his own company in Oregon, started researching and designing the finest softball bat he could, and by 1996 was manufacturing "softball's first customized high tech double-wall bat for the masses."
Design
The inner barrel of a double-wall bat is comprised of two ultra-thin walls close to--but independent of--each other. The purpose of the inner wall is to support the outer wall--but only after the outer wall has absorbed the impact of the ball prior to snapping back out. According to Softball Pitch, the inner wall "aids the durability and power of the bat as it creates a rebound effect when the ball is struck."
Construction
According to its inventor, DeMarini Softball Bats, double-wall technology "employs two independent alloy walls to create a dynamic, springboard hitting surface. Double-wall construction absorbs, holds and releases energy like a trampoline." Its construction is also designed to produce "a larger, more responsive sweet spot"--the optimum area of the bat barrel for hitting.
Trampoline Effect
The trampoline effect--present in all metal bats--propels the ball faster and farther from the barrel than wood. Dan Russell, Ph.D., professor of applied physics at Kettering University, describes it this way: "The barrel of the bat essentially acts as a spring during the bat-ball collision. If the barrel spring is very stiff, the ball compresses a great deal upon impact and loses a significant amount of energy in the process of compression and re-expanding. However, if the barrel of the bat is made softer, the barrel compresses more, the ball compresses less, and the ball loses less energy during the collision. Furthermore, the energy which was temporarily stored in the barrel spring is returned to the ball, and the ball speed is greatly increased after the collision."
Manufacturing Materials
The trampoline effect is unique to hollow-metal and composite bats--and double-wall bats are built from aluminum, aluminum alloys and composite materials. The aluminum is "aircraft-grade," and variations strengthening the alloy formula have allowed manufacturers to design bats with thinner shell walls. According to Epinion.com, "Manufacturers use advanced alloys to make the walls of the barrel of the bat thin while still allowing the bat to be strong enough to resist denting"--and capitalize on the trampoline effect--when bat strikes ball.
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