The Smartwool Men's Active Ultralite Short Sleeve is engineered to keep you cool, dry, and comfortable during your most intense, high-output pursuits. Crafted from a featherweight blend of ZQ-certified Merino wool and Tencel™ Lyocell performance fibers, this shirt delivers unparalleled breathability, rapid moisture-wicking, and natural odor resistance. With an athletic fit and thoughtfully designed offset shoulder seams, it eliminates chafing under backpack straps, making it the ultimate base layer for warm-weather trail running, hiking, and intense gym sessions.

Specifications

Technical Specs

• ​Model Number: SW016544
• ​Fit: Regular / Athletic (Moves with your body without feeling overly restrictive)
• ​Weight: Ultralight (Designed for maximum breathability in hot climates)
• ​Material Composition: ~53% ZQ-certified Merino Wool, 47% Tencel™ Lyocell (exact blend may vary slightly by production run)

​Key Features

• ​Merino & Tencel™ Blend: Combines the natural thermoregulation and odor resistance of Merino wool with the cooling, quick-drying softness of Tencel™ Lyocell.
• ​Offset Shoulder & Side Seams: Strategically shifts seams away from high-friction areas to completely eliminate chafing when wearing a hydration vest or heavy backpack.
• ​Flatlock Seam Construction: Minimizes bulk and provides a smooth, next-to-skin feel that prevents irritation during repetitive, high-intensity movements.
• ​Odor Resistance: The natural properties of Merino wool trap odor-causing bacteria, keeping you fresh even after grueling uphill climbs or multi-day use.
• ​Reflective Elements: Adds a touch of visibility for low-light conditions during early morning or evening runs.

​Care Instructions

​To maximize the lifespan of this ultralight performance fabric, follow these guidelines:

• ​Wash: Machine wash cold on a gentle cycle. Wash inside out to protect the outer face of the fabric from snagging or pilling. Wash with similar colors.
• ​Detergent: Use a mild liquid detergent. Never use fabric softeners or bleach, as they will coat the performance fibers and destroy their ability to wick sweat and regulate temperature.
• ​Drying: Tumble dry on low heat, or line dry in the shade for the best results and to extend the life of the garment.
• ​Ironing/Dry Cleaning: Cool iron if necessary, but do not iron over logos or reflective elements. Do not dry clean.

​X-Boundaries Professional Tips

• ​The Summer Base Layer Secret: Don't let the word "wool" scare you away in the summer. The addition of Tencel™ makes this ultralight fabric incredibly cool to the touch. It actively pulls sweat vapor away from your body before it condenses, making it far superior to pure synthetics in sweltering heat.
• ​Built for the Pack: If you are a backpacker or trail runner, you know the pain of collarbone chafing from shoulder straps. The offset seams on this shirt specifically target that issue, providing a smooth barrier between your skin and your pack.
• ​Travel Smart: Because of its incredible odor resistance and featherweight packability, this is the ultimate travel shirt. You can hike in it all day, hang it up to air out overnight, and wear it casually the next day without it smelling like a locker room.