In the old days, they used hickory. And then for many years it was ash. Now , most bats are made of maple (ash too). They seem to have a little more po p. But maple often shattered, endangering players and fans. They changed th e specs a little bit and use a dye to make sure the bat makers can find the smaller veins in maple. There were far fewer shattered maple bats in the M LB this year.