Gear Guy

Does a sleeping bag's "down fill" really matter?

I would like to know what the difference is between Marmot's 800-fill Couloir and 600-fill Never Summer sleeping bags if they both have a rating of zero-degrees. I'm going to Patagonia in January and would like to know which bag you would use, although I'm not yet sure what elevation I'll be at. Hans Norton, Massachusetts

A: It's true—one bag can have 600-fill down, the other 800-fill down, yet they both have the same temperature rating. The 600-fill down will cost less, too. The Never Summer you mention sells for $250, the Couloir for $490. A substantial difference. So why buy one over the other?

Mainly because an 800-fill bag requires less down to give you the same insulation, so it weighs less. In a 32-degree bag the difference is negligible, but in bags rated to zero or lower it starts to add up (more on this momentarily). Such a bag will also compress more, taking up less space in your pack. And, as a general rule, a higher-fill down is a better-quality down, with more fully developed down plumules. So it will last longer and withstand more stuffings and unstuffings than a 600-fill bag.
When comparing the Never Summer and Couloir bags, the down is not the only thing that has an effect on the weight and price. The Couloir is clearly a higher-end bag, with better and lighter materials. Bottom line: the Couloir weighs 3 pounds, 6 ounces, the Never Summer 3 pounds, 12 ounces. Not a huge difference, but for weight-conscious campers and climbers perhaps a worthwhile one.

Overall, I'd say a zero-degree bag should be fine for Patagonia, unless you go to quite high elevations, in which case a minus-ten bag might be better.

Our mission to inspire readers to get outside has never been more critical. In recent years, Outside Online has reported on groundbreaking research linking time in nature to improved mental and physical health, and we’ve kept you informed about the unprecedented threats to America’s public lands. Our rigorous coverage helps spark important debates about wellness and travel and adventure, and it provides readers an accessible gateway to new outdoor passions. Time outside is essential—and we can help you make the most of it. Making a financial contribution to Outside Online only takes a few minutes and will ensure we can continue supplying the trailblazing, informative journalism that readers like you depend on. We hope you’ll support us. Thank you.
Contribute to Outside
More Gear