If you do activities like tennis, mountaineering, skiing, mountain biking, and you need a piece of clothing to keep you warm, not cold, and not sweaty, this is exactly what will help you in the constantly changing weather. Hot cold, cold hot. Buy it with your eyes closed. Even at work, generally the [fleece vests] are ideal for the constantly changing weather. Every minute, half an hour. I wear a large, big chest, and it fits me just fine.