What Our Gearhead(R) Experts Are Saying:"This sleeping bag is a backpacker's dream-it's warm, versatile, and easy to customize. The WarmZip feature lets me fine-tune the shape and temperature, and the arm holes add so much livability. Plus, it's light enough for the trail and super cozy for chilly nights."From frosty spring mornings to crisp fall evenings, the Therm-a-Rest Boost 650 Sleeping Bag keeps us warm, comfortable, and ready for whatever the trail brings. Its semi-rectangular shape offers plenty of space to stretch out, while the innovative WarmZip(TM) system transforms the bag into a mummy shape, boosting warmth by up to 10degF when temperatures drop. With hydrophobic 650-fill RDS-certified down and Zoned Insulation, the Boost efficiently distributes heat where it's needed most, ensuring every night is cozy. Multi-use arm holes enhance ventilation and functionality, letting us adjust the bag or reach for our headlamp without leaving its warmth. Lightweight and packable, the Boost 650 is perfect for backpacking adventures. Its eco-friendly shell and liner, crafted from 100% recycled nylon with PFAS-free DWR coating, add a sustainable touch to its exceptional performance. Whether we're side sleeping, lounging in our tent, or stargazing, this bag delivers three-season comfort like no other.