Traditional single- and double-walled aluminum bats have been around for decades, but as bat companies have improved their products, they have incorporated alloys, mixes of substances like aluminum, magnesium or zirconium, to make a better product.
The first attempts at composite bats involved a mixture of plastic and graphite, but those attempts in the 1980s did not outperform traditional aluminum bats. It has only been in about the past 10 years that graphite, aluminum composite bats have become popular.
Composite bats balance the distribution of weight in the bat to get more weight toward the handle so bat speed is easier to generate. Alloy bats are an improvement on traditional aluminum bats because they accomplish a similar result by making the bat lighter and allowing for the generation of increased bat speed. Studies by the NCAA and Little League Baseball indicate that the speed of the ball off the bat is better off of a composite bat than from an aluminum or alloy bat.
One of the major differences between composite and alloy bats is the breaking-in period required with composites. In order to achieve the best results, it is necessary to hit up to 150 balls with your composite bat to get it ready for live use. Also, composite bats tend to cost about 25 percent more than the most expensive alloy bats. With the increasing use of alloys in the aluminum bats, that gap in bat performance is closing, but there is still the consideration of cost of replacement when decisions are being made on which bat to buy.
Composite bats are not allowed by the National Collegiate Athletic Association (NCAA) and therefore can't be used in college baseball games. The NCAA ruled that the increased speed of balls off of composite bats is a cause for safety concerns.
The first attempt at the creation of an alloy-type bat was the 1990s experiment with titanium bats. The performance of these bats was significantly superior to aluminum bats then in use, but it was so superior that the bats were quickly banned by almost all organizations due to safety concerns. Since then, the development of new bats using different alloys have begun to provide additional options.