SEATTLE — Major League Baseball parks are storing baseballs in humidors before games this season as a way to create consistency in ball quality. The new standard began in 2022 for all 30 teams.
Alan Nathan, a retired professor of physics at the University of Illinois, studies how balls can change in different environments.
“By storing it in a humidor, that helps even out not only from one ballpark to another but throughout the season,” explained Nathan. “It keeps the properties of the ball constant.”
Nathan said the goal is to have an even playing field for all teams at all ballparks, and a big factor in that equality is the ball itself.
“You have to remember, a baseball, much of it is machine-made, but a lot of it is handmade, and whenever things are handmade out of organic materials, you’ve got cotton thread and leather from cows, and not all cows are the same,” said Nathan. “So, you’ve got materials that are not necessarily constant, that are organic materials, and they can change. So, for me, it’s always quite surprising that the baseball is as constant as it is, and it takes a lot of effort to get it that way.”
When it comes to the balls and new humidors, the environment they’re stored in can be controlled, but there are outside factors that can still impact the ball and, ultimately, the game.
Nathan said this change is because of the ball's density, and that depends on how the ball was stored before the humidors. The humidors keep balls at 70 degrees and 57% relative humidity.
If a city has an environment with higher humidity than that 57% threshold, the humidor will lower the humidity of the ball, and the bounciness of the ball would increase. In theory, that could cause the ball to go farther and potentially lead to more home runs in those cities.
The opposite is true for dry climates. If a city’s humidity is lower than the 57% threshold of the humidor, the humidor would increase the humidity and density of the ball. That decreases the bounciness of the ball and as a result, causes the ball to not be hit as far in a game.
The Seattle Mariners and Houston Astros are currently in the middle of the American League Division Series. The potentially five games are split between Houston and Seattle, two cities with different climates.
With Seattle’s currently dry weather and mild temperatures in the 70s, the humidor’s conditions are not far off from the city’s weather, meaning the humidor wouldn’t have a major impact on the game.
In Houston, daytime heat is getting up to around 90 degrees, and humidity is high, so the humidor would drop both temperature and humidity. However, the roof closes at Minute Maid Park and the temperature inside the ballpark is controlled at 73 degrees. So the difference between the humidors versus the environment is also not as high.