A composite bat is constructed using a combination of carbon, Kevlar fibers or glass that is melded into a plastic resin base. The resin serves as a bonding agent that holds the various materials together.
As of 2015, most brands of composite bats require a breaking-in period to allow it to reach maximum efficiency. A typical composite bat requires between 150 to 200 swings to allow the material in the bat to break down and become ready for use during baseball games. Most types of composite bats are not recommended for use in cold weather, as it could lead to a drop in bat performance.