Women's Icebreaker Siren M Thermal Shirt - Black, Medium

On a crisp morning trail run or a long day of travel, the Icebreaker Siren M thermal shirt keeps you comfortable without bulk. This slim-fit base layer is cut for women and made from a Corespun blend of 83% merino wool, 12% nylon, and 5% LYCRA®, giving you softness, durability, and stretch in one piece. The sweetheart neckline and drop-tail hem add a feminine, functional touch, while flatlock seams prevent chafing under layers.

Key specifications

• Material: 83% Merino Wool, 12% Nylon, 5% LYCRA® (Corespun fabric, 150 g/m²)
• Fit: Slim, with sweetheart neckline and drop-tail hem
• Sleeve length: Long sleeve
• Seams: Flatlock to reduce friction
• Odor resistance: Natural merino wool
• Breathability: High
• Moisture wicking: Yes
• Temperature regulation: Yes
• Wool sourcing: Mulesing-free
• Colour: Black
• Size: Medium (M)

Why choose it

Merino wool naturally regulates temperature, wicks moisture, and resists odors, so you can wear this shirt multiple times between washes. The Corespun construction wraps merino around a nylon core for added strength, while LYCRA® provides stretch that moves with you. It's an all-season base layer that works as well under a ski jacket as it does on its own in mild weather.

Ideal use cases

• Hiking and backpacking
• Travel and commuting
• Everyday layering in cool weather
• Winter sports base layer
• Active outdoor adventures

Good to know

The Siren M is part of Icebreaker's core base layer range, known for its lightweight warmth and next-to-skin comfort. It's machine washable on a gentle cycle, but avoid fabric softeners to preserve wool performance. The drop-tail hem provides extra coverage when bending or reaching.