The Merino 125 Cool-Lite Sphere Long-Sleeve T-Shirt blends merino wool with TENCEL Lyocell at Icebreaker's lightest warmth rating, so it works as a standalone layer instead of an under-layer piece. Offset shoulder seams keep pack straps and pole grips from creating friction points, and side splits at the hem open up mobility and airflow on long climbs. The drop tail hem adds coverage without adding bulk, so the shirt moves the same way whether it's a solo run or a full day on the trail. What Our Gearhead(R) Experts Are Saying:"I wore this on a July trail run where I'd normally sweat through a heavier merino tee by mile three, and the 125-weight fabric stayed breathable the whole way. It dries fast enough on the hike out that I never noticed it was damp."