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, lightweight insulation material initially designed for NASA, you never have to worry about warmth.

The all-new medial zipper provides easy on/off, a new improvement made directly from customer feedback. Merrell waterproofing on the upper will keep your feet dry. With Vibram IceTrek underfoot, traction remains consistent under the wettest, most slippery conditions. For the first time ever incorporating Vibram traction lug for enhanced grip on uneven terrain.

FEATURES
Waterproof membrane seals out water and lets moisture escape
Waterproof full grain leather and knit upper
100% recycled laces and webbing
Heavy-duty, Waterproof, YKK medial zipper for easy on and off
Bellows tongue keeps out debris
Protective and abrasion resistant rubber heel and toe cap
100% recycled fleece lining
200 grams Primaloft Gold Eco Series synthetic insulation
SOLARCORE Aerogel insole provides underfoot superior warmth while being extremely flexible and ultra-thin
100% recycled mesh footbed cover
Cleansport NXT treated for natural odor control
5% recycled removable PU footbed
FloatPro Foam midsole for lightweight comfort that lasts
Vibram Icetrek outsole designed to provide the improved grip on very cold, icy, or snowy surfaces
Vibram traction lugs specifically designed to increase traction and shed debris with each step