Women's Siren 4 Thermo Mid Zip Waterproof

Built specifically for women and engineered for cold-weather adventures, the Merrell Siren 4 Thermo Zip delivers warmth, stability, and confidence on winter trails and icy terrain. Backed by 25 years of Merrell’s women’s-specific fit, this boot is designed to cradle the unique contours of the female foot for lasting comfort and support—even on long hikes.

With 200 grams of insulation and advanced SOLARCORE® Aerogel technology, originally developed for NASA, the Siren 4 Thermo Zip provides exceptional warmth without added bulk. Merrell’s waterproof membrane seals out moisture while allowing breathability, keeping feet dry in wet, snowy conditions.

A newly added medial waterproof YKK zipper makes getting in and out effortless—an upgrade inspired directly by customer feedback. Underfoot, the Vibram® IceTrek outsole with specially designed traction lugs delivers reliable grip on icy, snowy, and uneven surfaces, ensuring confidence with every step.

Key Features:

• Waterproof membrane seals out water while allowing moisture to escape
• Waterproof full-grain leather and knit upper
• Heavy-duty waterproof YKK medial zipper for easy on and off
• 200g Primaloft® Gold Eco Series insulation for warmth
• SOLARCORE® Aerogel insole for ultra-thin, flexible thermal protection
• Bellows tongue keeps out debris
• Protective rubber heel and toe cap for durability
• Cleansport NXT™ treatment for natural odor control

Comfort & Sustainability Details:

• FloatPro™ Foam midsole for lightweight, long-lasting comfort
• Vibram® IceTrek outsole for superior traction on cold, icy surfaces
• Vibram® traction lugs enhance grip and shed debris
• 100% recycled laces, webbing, fleece lining, and mesh footbed cover
• 5% recycled removable PU footbed

Performance Specs:

• Stack height: 28.5–20.5 mm
• Drop: 8 mm
• Lug depth: 5 mm
• Half pair weight: 1 lb 3.04 oz (540 g)

Designed for winter hiking, snow-covered trails, and cold-weather exploration, the Merrell Siren 4 Thermo Zip delivers warmth, traction, and women-specific comfort you can rely on.