Compact And Superlight, Our Lightest Atom Vest Easily Stashes In Your Pack, Ready To Grab When Summer Temperatures Drop. Worn As A Midlayer Or Standalone, It Delivers Moderate Insulation Perfect For Early Morning Runs And Taking In The View From A Freshly Bagged Peak. The Tyono™ 20 Shell Balances Breathability And Wind Resistance, And The Coreloft™ Insulation Is Light, Compressible, And Efficient. Lightweight Stretch Fleece Side Panels Improve Ventilation And Hold The Fit.