Partway through a training session, when the pace shifts and body heat shifts with it, the Swix Polaris Baselayer 1/2-Zip Top counts on 100% merino wool to regulate temperature and moisture. Flatlock seams reduce friction for a smooth feel against the skin, and a chin guard rounds out the neckline of this merino base layer. What Our Gearhead(R) Experts Are Saying:"When my pace picked up during training, I unzipped the neckline and the heat left within a few strides. Zipping it back up once I eased off kept the warmth in, so the same top handled both stretches."