Men's and Women's Altitude Thermal Base Layers

The Altitude Collection is where it all started for io and includes some of our all-time best sellers like the Women's Altitude Crew and the Men's Altitude Zip. Originally designed for snow and on-mountain sports, this range quickly become our jack-of-all-trades, go-to thermal base layer. With 96% superfine, temperature regulating merino and a snug, contact fit, the Altitude Range is the perfect lightweight thermal layer for core warmth when you’re layering up, but just as comfortable worn on its own in milder conditions if you don’t mind a figure hugging fit. (If you’re looking for all the performance in a regular or casual fit, try our Ultra or Universal ranges!) Which is why people who know, go with io. Because it’s incredible outside.