Icebreaker W SIREN LS SWEETHEART Long-Sleeve T-Shirt

Designed for women looking for a lightweight and versatile base layer, the Icebreaker W SIREN LS SWEETHEART long-sleeve T-shirt is perfect for hikers, snow sports enthusiasts, yoga practitioners, and travelers alike. Its slim fit and corespun fabric—made from an 83% merino wool blend—make it both functional and comfortable for everyday wear. Weighing just 123 g, it integrates seamlessly into a layered outfit without adding bulk.

The W SIREN LS SWEETHEART: Technical Fabric for Thermal Comfort

The fabric’s composition is based on a corespun construction that combines merino wool with nylon and LYCRA®, a technique that wraps synthetic fibers around a merino core. This process enhances the fabric’s durability while preserving the characteristic softness of the natural fiber. With a micron count of 18.9 µ, the wool used is fine and gentle on the skin. The lightweight weight of 150 g/m² places this T-shirt in the ultralight category, making it ideal as a base layer for mountain outings or snow sports.

Thermal regulation is one of merino wool’s natural strengths: the fabric helps maintain a stable body temperature, whether in cold weather or during heat-generating activities. The fabric’s moisture-wicking and breathable properties contribute to this active comfort by limiting the buildup of sweat against the skin during physical activity.

Natural properties suited for active pursuits

Merino wool naturally offers odor-resistant properties thanks to its fibrous structure, which reduces bacterial growth even after several hours of activity. This feature is particularly appreciated during travel or extended outings where washing options are limited. The fabric also provides natural UV protection—an inherent property of merino fiber—which is useful during high-altitude or outdoor activities. The inclusion of LYCRA® in the blend provides stretch that moves with you without restriction, whether you’re doing a yoga session, a hike, or a day of skiing.

Care and Material Commitments

The merino wool used is certified to the Responsible Wool Standard (RWS), a certification that guarantees responsible practices in flock management and agricultural land use. To preserve the fabric’s qualities over time, machine wash on a warm cycle, inside out with similar colors, without fabric softener or tumble drying. Line-drying in the shade is recommended, and if ironing is necessary, use a warm iron and avoid pressing directly on any prints.

The Icebreaker W SIREN LS SWEETHEART long-sleeve T-shirt is available in Midnight Navy, in sizes S, M, and L.