From the Toronto Globe and Mail ( behind a paywall), by Cathal Kelly: The first baseball uniforms were made of coarse wool. Cotton would have made more sense – cheaper, more breathable – but those initial haberdashers of the diamond wanted to look like proper business types. That also explains the first hats, which were made of straw. Before the invention of the elasticated boxer-brief and the athletic support, one can imagine what it must have felt like to throw a hundred pitches in form-fitting burlap. This must be why old-timey pitchers in the movies are always angry. Amazingly, the baseball uniform hasn't changed much in the nearly 200 years since. It remains an impractical sports-business suit. You watch a guy slide headfirst into second base – pretty standard baseball stuff – and he will rise in a state of dishevelment. His shirt has been pulled out of his pants. His pants have started to corkscrew around his waist. Everything's akimbo. This problem is worse if the player is carrying a little extra baggage around the middle. God help that guy if he has to leg out a triple. By the time he gets to third, his uniform will have essentially worked its way off him. Then he has to get redressed in front of 40,000 people. Imagine if it worked this way in other professions where people wear uniforms – ‘Sorry, I need a minute before I go into that burning building, chief. My shirt's all funny.' So when Major League Baseball and its equipment partners decided to rethink the uniform, there was room for innovation. The real upshot is that the uniforms are lighter. I'm not sure 18 ounces of broadcloth is what's preventing the average shortstop from mashing like Mark McGwire, but let's imagine that's possible. Lighter fabric is also thinner. These new uniforms are so performance-enhanced that they become see-through under a hot flash. The rest of the article is long, and funny. If you can get past the paywall, it is worth a read. https://www.theglobeandmail.com/sports/article-baseballs-new-jerseys-were-designed-for-the-long-con-of-sports/https://www.theglobeandmail.com/sports/article-baseballs-new-jerseys-were-designed-for-the-long-con-of-sports/ Later