I was tired of wearing 4 layers when touring so I finally paid for a good base layer. By far the best investment in my clothing system. If you plan to hike or tour a lot, you will sweat a ton no matter how cold it is. I usually wear a wicking shirt over this to get the moisture away from my body. Also, Under Armour designed these to not be a real tight fit, it shouldn't fit like spandex. I usually wear a large but had to get an extra large for mine to properly fit my arms. I'm 6'1" and 150lbs. Seriously the best base layer you can buy.