A good base layer is like a good pair of tires. If you're going to make it up the hill on a day where it snowed 16in overnight, you need to have a good set of tires, with at the very least decent tread, to make it safely. Meaning, if you're going to make it you need to at least give yourself a chance at success. Also the same as shooting a basketball, you have to put the ball above the rim for it to have a chance of going in. How does that relate to a baselayer? Well, in order to properly regulate body temperatue you need to at least give yourself a chance. Synthetics are great for hot or cold, but they end of smelling...ripe. The thing I love most about merino wool is that 1) it doesn't smell bad, ever, 2) it's far more comfortable than any other base layer material, and 3) it regulates body temperature better than other base layer materials, in my opinion. This layer is great cause it's not too heavy and can be worn in multiple applications. Comfort is #1, smell is something you can deal with if a piece of clothing is comfortable and if it does it's job of regulating body temperature, but comfort is not. This piece meets my prerequisites of comfort, smell, and various applications. Needless to say, Icebreaker makes one hell of a merino base layer. Highly recommend.