http://arxiv.org/abs/0712.0380 Influence of a humidor on the aerodynamics of baseballs Edmund Meyer, John Bohn 17 pages, 6 figures (Submitted on 3 Dec 2007) "We investigate whether storing baseballs in a controlled humidity environment significantly affects their aerodynamic properties. To do this, we measure the change in diameter and mass of baseballs as a function of relative humidity (RH). We then model trajectories for pitched and batted baseballs to assess the difference between those stored at 30% RH versus 50% RH. The results show that a drier baseball may be expected to curve slightly more than a humidified one, and that the drier ball will also likely travel slightly less far when batted. We discuss consequences of these results for baseball played at Coors Field in Denver, where baseballs have been stored in a humidor at 50% RH since 2002." I would surmise that drier balls favor the pitcher, if they indeed take a curve better and, when hit, don't go as far. Conversely, damper balls might be supposed to favor the batter. EDIT: I got the effect backwards. Pitchers like the damper balls. I was under the impression that humidors were originally invented to store cigars, back in the days of serious cigar-smoking. Here is another use for humidors.