Comfort doesn't have to be sacrificed for performance, and the Sonic certainly delivers on both. The Nemo Sonic is a high-performance ultralight mummy sleeping bag designed for mountaineers, winter backpackers, and alpine climbers who demand reliable warmth in extreme conditions. Built to handle everything from deep winter bivvies to high-altitude expeditions, it combines premium insulation, advanced temperature control, and rugged construction into one highly adaptable sleep system. Engineered as a true big-mountain sleeping bag, the Sonic is designed to perform across a huge temperature range, from mild conditions down to serious sub-zero expeditions. Its award-winning design delivers exceptional warmth and protection in harsh alpine environments. One of the Sonic’s standout features is its second-generation Thermo Gill™ vents, allowing you to fine-tune temperature without exposing yourself to cold drafts. Multi-stage zip system expands the usable temperature range. Vent excess heat during milder conditions and retains warmth when temperatures drop. This makes the Sonic incredibly versatile, effectively replacing multiple sleeping bags with one adaptable system. Filled with 800 fill power hydrophobic down, the Sonic delivers outstanding warmth-to-weight performance: High loft for efficient heat retention. Moisture-resistant treatment for damp mountain conditions. RDS-certified for responsible sourcing paired with chevron baffle construction, the insulation stays evenly distributed, eliminating cold spots and preventing down migration. Built for real-world winter expedition conditons, every detail is designed for durability and performance. More Help? For further assistance on choosing your down sleeping bag, we have an article explaining fill power, the pros and cons of down over synthetic insulation and more info on caring for your bag available to view here: A Guide to Down Sleeping Bags. Features Award-winning design updated for even greater warmth retention and adjustability across temperatures. Second-generation Thermo Gill™ vents extend the comfort range with a new multistage zipper system. Chevron baffle construction better compartmentalizes down for more uniform loft and down migration prevention. Toester™ waterproof/breathable footbox utilizes a layer of synthetic insulation to protect the down and deliver maximum toastiness for toes. Constructed with bluesign® approved 100% recycled shell and liner fabrics. Filled with premium 800 FP hydrophobic, PFAS-free, RDS-certified down. Products certified to the Responsible Down Standard (RDS) contain down or feathers from farms certified to animal welfare requirements. Stretch construction at the knees for comfortable side sleeping. Offset zipper creates a thermally efficient seal while an updated profile secures warmth closer to the body. What's included: Compression Sack, Mesh Storage Cube. Specification Intended use: Winter backpacking, camping and Alpine mountaineering Season Rating: 4 season. Sleeping bag Weight: Regular: 1.47kg / Long: 1.62kg Maximum User Height: Regular: 183cm / Long: 198cm Comfort Temp: -10°C Comfort Temp Limit: -18°C Down treatment: Hydrophobic, PFC-Free Down Max Shoulder Circumference: Regular: 160cm / Long: 165cm Shell Fabric: 20D 100% Recycled Nylon, Bluesign Certified Ripstop w/ DWR Lining: 20D 100% Recycled Polyester, Bluesign Approved Taffeta w/ DWR Footbox Fill power: 800 FP Down Fill Weight: Regular: 790g / Long: 835g Compression Size: Regular: 34 x 24 cm / Long: 36 x 24 cm Zip Configuration: Left Colour: Goodnight Gray / Goldfinch Cut: Mummy
