I've been wearing Merino wool since 1982, not always on a bike but always in extreme cold. Not only does Merino absorb a lot of sweat, it also holds your body heat. The problem with cotton is that is absorbs sweat and then gets cold. Finding 100% Merino wool today is not easy since they use synthetics to stich the parts together. I've found 90% locally but it is quite expensive. Silk is also very good for keeping you dry, but then you need something on top to keep you warm. As far as washing goes, I wear that stuff once and then is gets washed. Stink is not the only issue: Bacteria can become an issue as well.