What Our Gearhead(R) Experts Are Saying:"This is my pick for hot, hard efforts when every gram matters. It's incredibly light, breathes better than almost anything else I've worn, and the seam placement really does reduce chafing over long runs. Perfect under a vest or worn solo in the heat."When the sun is high and the pace stays fast, we rely on the Sonic Ultra Vest to keep us cool and focused. Built by Rab for mountain runners and fast hikers, this ultralight layer strips things down to the essentials, delivering maximum airflow and comfort for high-output days in the heat. The Motiv(TM) Aero fabric uses a subtle mesh structure and bulk yarn technology to wick sweat quickly and dry fast on steep climbs. Laser-cut vent holes dump excess heat from high-sweat zones, while carefully positioned seams and a racerback design reduce friction over long distances and sit comfortably under a hydration pack. Whether we're chasing vert or logging hot trail miles, this vest is the minimalist layer we trust when conditions demand breathability above all else.