For the first time MLB is storing baseballs in humidors at all 30 ballparks this season. Last year 10 teams used the humidor in their home ballpark: the Astros, Blue Jays, Cardinals, Diamondbacks, Mariners, Marlins, Mets, Rangers, Red Sox, and Rockies. Now all 30 clubs have a humidor, and the humidor brings the ball to average humidity. It dries out the ball in humid climates and "wets" it in dry climates. The drier the baseball, the more it flies.
Using the humidor in all 30 parks brings consistency to the baseball, at least in theory. There are so many variables in play that are impossible to quantify. How the ball is transported from the Rawlings factory in Costa Rica to each MLB city, how long the ball is stored in the humidor, and all sorts of other stuff matters quite a bit. Every time a baseball warms up and cools down, its physical properties change. Everything in the ball (the leather, the cork, etc.) experiences wear and tear, for lack of a better term.