Well, it's not a deal-breaker, but it's not its strongest suit either. The shoe offers decent breathability but might not be the best choice for extremely hot conditions. If you're running through a sauna (or just a really hot day), you might want to consider the Asics FujiSpeed. I got this shoe for my husband, and I can tell you, it's a game-changer. It's lightweight, has a half plate for that extra snap, and the synthetic upper is so breathable you can literally see right through it.