With 25 years of Merrell's women's-specific fit, the Siren 4 Thermo is uniquely engineered to cradle the distinct contours of female feet, providing comfort, support, and stability even on the longest hikes with 200 grams of added insulation for warmth and protection.

Now equipped with SOLARCORE insulation, it's a lightweight insulation material initially designed for NASA, you never have to worry about warmth. The all-new medial zipper provides easy on/off changes.