Nemo's Sonic™ series has been praised as the only bag you really need all the way from -20 to 40 degrees Fahrenheit. Their proprietary Thermo Gill™ vents allow you to release heat on milder nights, vastly extending the comfort range. Stretch stitching in the legs minimizes extra air volume you need to heat up.
Waterproof/breathable fabric over the footbox protects against frost and condensation on tent walls. Over-stuffed with 800FO hydrophobic, RDS certified down, Sonic™ is fine-tuned for frigid weather.
