What Our Gearhead(R) Experts Are Saying:"I wore this under a shell on a chilly morning trail run and never had to think about temperature again, it just adjusted as I warmed up. The slim fit meant it stayed put under a jacket without bunching or riding up."Backcountry Romantic CopyThe Anatomica Tank Top from Icebreaker earns its spot as a base layer for the days that swing between cold starts and warm afternoons. We've reached for it under a jacket on brisk mornings and worn it alone once the sun climbs higher, and the merino corespun fabric keeps pace with the shift every time. The slim fit stays close to the body without restricting movement, whether that means reaching overhead on a climb or settling into a steady rhythm on a long run.