(updated: )
The subject of bat construction and materials became significant in 2009 and 2010 when certain composite-barreled bats were found to exceed league ratings for rebound. Excessive rebound can lead to injuries during a game. Little League International enacted a ban on composite-barreled bats in 2010. In January (2011) Little League International released lists of approved composite-barreled bats and will continue to update same as more testing is accomplished.
The Little League International web site links
to bats that HAVE BEEN APPROVED are:
approved wooden bats.
approved non-composite-barreled non-wooden bats.
approved composite-barreled bats
for Major League Baseball Division and below (ie, Big Flats).
approved composite-barreled bats
for Junior, Senior and Big League Baseball Divisions only
(This affects Big Flats Senior League Division.)
BBCOR bats: Required for college and high school play as of the 2011 season. To my knowledge (based on a search of their web site this morning), Little League International has not yet formally addressed the issue of BBCOR bats. According to Q-12 (Question 12) in the FAQ section of the latest update to the Moratorium Letter, BBCOR-compliant bats will be required for Junior, Senior and Big League play in 2012; and, such bats are legal for play in the 2011 season.