The Altitude Collection is where it all started for ioMerino and includes some of our all-time best sellers like to 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. The Altitude Range is the perfect lightweight thermal layer for core warmth when you’re layering up, yet versatile enough to be worn on its own in milder conditions.