The new Marucci Cat 9 baseball bats are made with the all new, exclusive AZR Aluminum alloy – which Marucci says is the highest grade aluminum ever put into a baseball bat. The Cat 8 uses the AZ105 Aluminum alloy, which is still an ultra high performance material for bats. The new AZR alloy is supposed to be lighter, stronger, more durable, and ultimately give a better feeling on contact, and farther hit baseballs.
The other major difference (for the Cat 9 BBCOR model only) is the Cat 9 BBCOR has grooves carved into the barrel of the bat on the inside, these grooves run a horizontal (knob to end cap) direction across the sweet spot of the bat and make the walls thinner, more responsive, and overall perform better by increasing the size of the sweet spot.