If you want a warm layer with the option for temperature control, look no further than the Smartwool NTS Midweight 250 Zip Top. In the unlikely circumstance that the Merino wool of this top can't regulate your skin temp, just unzip for an instant cooling effect. Not that you'll even need to do that, since the Smartwool NTS Midweight 250 Zip Top is a moisture wicking machine, designed to regulate your body temperature. This thing works wonders as a base layer, and has flat seams constructed for ultimate comfort, so you don't have to worry about chafing under all that gear.