The NEMO Sonic 0 has a few versatility-enhancing tricks up its sleeve that make it ideal for four season camping in the mountains. The 800 fill down gets a hydrophobic treatment that enhances its warming properties should it get wet, and it’s guaranteed cruelty free, thanks to its Responsible Down Standard (RDS) certification. Stretch panels at the knees give superior freedom of motion for adjustments mid slumber. But the real star of the show is arguably Nemo’s adjustable Thermo Gills™, which allow the Sonic to vent excess heat while simultaneously blocking out cold drafts. In other words, you get to fine tune how warm your bag is without having to fully unzip. And that means more comfort to help you sleep deeply through the night, especially in the summer months.