Compression testing measures the amount of pressure it takes to compress the barrel of a bat 1/4". The less pressure it takes to compress the bat, the easier it is to achieve maximum trampoline effect when the ball makes contact with the bat. Composite barreled bats will get easier to compress the more they are used. This is why there is a "break-in" period on most composite bats. Below we have tested a number of bats for you to compare. The bats used in these tests are brand new with zero hits on them.