New Standard to be implemented for the 2018 season – Read More about this here:

http://www.littleleague.org/media/llnewsarchive/2015/May-August/Little-League-USA-Baseball-Bat-Standard-2018.htm

Little League has updated all their information on bats for the upcoming season. Be sure to review for bats are legal as new penalties for illegal bats (automatic outs) are in place.

http://www.littleleague.org/learn/equipment/baseballbatinfo.htm

Here are some additional references on baseball bats:
http://ezinearticles.com/?What-is-a-Composite-Baseball-Bat?&id=1569771
http://sports.espn.go.com/ncaa/news/story?id=4351979