Buying A Sleeping Bag: Down vs. Synthetic

sleeping bagBuy­ing a sleep­ing bag can seem over­whelm­ing, but it doesn’t have to be. When you’re pick­ing the right bag for your next adven­ture, the first deci­sion is sim­ple: whether to buy down or synthetic.

How to Choose Your Insulation
There are two pri­ma­ry kinds of insu­la­tion: down (usu­al­ly made from a duck or goose’s plumage, or under­feath­ers) and syn­thet­ic fibers. Down is light­weight, breath­able, easy to com­press, and excels in cold, dry con­di­tions. Once down gets wet, how­ev­er, it pro­vides almost zero warmth and can take a very long time to dry—which can be a lia­bil­i­ty if you’re plan­ning a trip where wet weath­er is a con­cern. Syn­thet­ic insu­la­tion insu­lates when wet, dries very quick­ly, is hypoal­ler­genic, and is often cheap­er. But it’s also heav­ier, less durable, and bulkier.

Under­stand­ing Down
When you’re look­ing at down bags, the first step is to under­stand the con­cept of fill pow­er. You’ve prob­a­bly seen it on prod­uct labels: 700-fill down, 800-fill down, etc. But do you know what those num­bers actu­al­ly mean?

There’s a com­mon mis­con­cep­tion that fill pow­er is the amount of down in a bag, but it’s actu­al­ly a ref­er­ence to the loft or fluffiness—and there­fore the quality—of the down that is used as insu­la­tion in the sleep­ing bag or anoth­er gar­ment. If you take one ounce of 700-fill down, it will hypo­thet­i­cal­ly take up 700 cubic inch­es; one ounce of 800-fill down will take up 800 cubic inch­es, etc. High­er-grade down (which is usu­al­ly made from more mature birds) is more expen­sive, but it will trap more air next to your body—and the bet­ter your bag’s warmth-to-weight ratio will be.

Under­stand­ing Synthetics
Syn­thet­ic insu­la­tion is usu­al­ly made of poly­ester. Most bags use one of two tech­nolo­gies: short-sta­ple fills or con­tin­u­ous-fil­a­ment fills.

Short-sta­ple fills use short strands of thin fil­a­ments that are dense­ly packed, which makes sleep­ing bags flex­i­ble, soft, and compressible—though not quite as com­press­ible as a down bag of sim­i­lar warmth. Con­tin­u­ous-fil­a­ment insu­la­tion uses longer, thick­er fil­a­ments that are less com­press­ible than short-sta­ple insu­la­tion, but more durable. All syn­thet­ic bags dry rel­a­tive­ly quick­ly, and most are sig­nif­i­cant­ly less expen­sive than down. Most impor­tant­ly, they’ll still insu­late when wet.

Decid­ing Factors
Most peo­ple know that down is ide­al in cold, dry cli­mates, where syn­thet­ic insu­la­tion per­forms bet­ter in wet envi­ron­ments. But there are oth­er con­sid­er­a­tions, too. Down is com­press­ible, where syn­thet­ics are usu­al­ly bulki­er. Down is more breath­able, but syn­thet­ic sleep­ing bags are eas­i­er to wash. And weight is a huge fac­tor: if you’re plan­ning a through-hike of the PCT, those extra ounces mat­ter much more than if you’re car camping.

For more help, ask an expert—and remem­ber, no mat­ter what kind of insu­la­tion you choose, always store your sleep­ing bags uncom­pressed, which main­tains loft and warmth.