French chemist Andre-Louis Debierne discovered the chemical element Actinium over 100 years ago, but you can thank Arc'teryx for developing its namesake product, the Actinium Sleeveless Shirt. Designed for trail running or mountain adventures in warm weather, the Actinium breathes exceptionally well and wicks moisture like nobody's business thanks to the proprietary Viente polyester micro-mesh. Fast-drying and cool-wearing, Viente fabric also comes with an anti-microbrial treatment, meaning you won't clear rooms after your run. Flatlocked seams eliminate chafing, allowing you to indulge your masochistic training regimen while keeping all of your skin in tact. When you hit the trails, bring along the Actinium Sleeveless Shirt and remember the French chemistï¿½or just enjoy the performance benefits developed by Arc'teryx, your choice.