High Quality Content by WIKIPEDIA articles! Composite baseball bats incorporate a recent advancement in the technology of aluminum baseball bats for high school and collegiate players. In general, composite bats are constructed with the same aluminum exterior as standard aluminum baseball bats, but have a "woven" graphite wall on the inside. Composite bats provide an advantageous swing weight, an improved trampoline effect, a lower bending stiffness, and a higher damping rate. Recently, composite baseball bats have come under scrutiny because tests performed by the NCAA during the 2009 NCAA Division I Baseball Tournament showed that the majority of composite bats used during the championship failed the BESR test.