When you’re shopping for a new sleeping bag or puffy jacket, one of the most important decisions you’ll have to make is between down and synthetic insulation.
The type of insulation directly affects the warmth, weight, water resistance, compressibility and price of sleeping bags and jackets. Both down and synthetic have pros and cons when it comes to performance, so choosing the right type of insulation for your use can turn a cold, uncomfortable outing into an enjoyable time outside.
Let’s take a closer look at down and synthetic insulation to help make your decision easier.
A common misconception is that down insulation is made from the feathers of a bird. Down is actually the plumage found underneath the exterior feathers on waterfowl such as ducks and geese and consists of soft, fluffy, wispy filaments. Some products use a blend of down and feathers, but by definition, down is different than feathers.
Down insulates by trapping air and is prized for being light, easy to compress, long-lasting and breathable. It’s the insulation of choice in cold, dry conditions, or whenever reducing weight and saving space are top priorities.
Down insulation has typically been sourced from geese. However, many major manufacturers switched to duck down in recent years due to the cost of goose down. All testing and performance standards are the same for duck down and goose down, so either way, you can be assured you’re getting a high-quality product. However, you’ll find that goose down is often still used in the highest-end products because it can reach a higher fill-power rating than duck down.
Fill power is the term used to measure down’s ability to loft and thus trap heat. It is calculated by how many cubic inches one ounce of down can fill in a testing device. For example, 600-fill-power down means that one ounce of that down fills 600 cubic inches of space. Premium goose down can reach 900 fill-power, and potentially even higher. Duck down can achieve fill-power ratings no higher than 750 or 800.
The advantage of higher-fill-power down is that sleeping bags and jackets require less down to fill space and achieve a certain temperature rating. Less down equals a lighter product. So a sleeping bag rated +20°F with 700-fill-power down will be lighter than a +20°F bag using 600-fill-power down (assuming the fabrics and other features are comparable in weight).
The most common criticism of down insulation is its tendency to clump up and lose loft when it gets wet, thereby losing its insulation properties. Proprietary technologies have been developed over the years to treat down at a microscopic level with a water-resistant application. This treatment allows down to resist light moisture without compromising loft. However, if submerged in water or exposed to heavy rain, even treated down will get wet, so do your best to keep your down-filled items dry.
- Higher warmth-to-weight ratio than synthetic insulation
- Very compressible
- Very durable; with proper care, a down sleeping bag or jacket can last for decades
- Loses insulating power when it gets wet and takes a long time to dry
- Cleaning down requires special care
- Not hypoallergenic (rarely an issue)
- More expensive than synthetics
Typically made of polyester, synthetic fill is quick-drying and insulates even if wet (something down struggles to do). It also tends to be less expensive than down insulation, and it's durable and hypoallergenic.
There are many competing brand names for synthetic insulations, which can make shopping confusing. A more relevant distinction is knowing whether a synthetic insulator is short-staple or continuous filament.
Short-staple insulations feature short strands of fine-denier filaments that are densely packed to minimize heat loss. This makes sleeping bags and jackets feel soft and flexible, much like down-filled products, and allows for great compressibility. They are, however, a bit less durable than continuous filament and the insulation can move around to create cold spots.
Continuous-filament insulations use a thicker continuous filament that is lofty, strong and durable. They tend to have a stiffer feel and are less compressible than short-staple insulations, but they stay in place so are less likely to create cold spots.
- Very water-resistant and continues to insulate even when wet
- Less expensive than down
- Heavier and bulkier than down insulation
- Offers less warmth for its weight than down
- Less durable than down; insulating power gets reduced each time the bag is stuffed into a stuff sack
Some manufacturers make sleeping bags and jackets with a combination of water-resistant down and synthetic insulation. This hybrid construction can provide the benefits of both materials while limiting each material’s imperfections.
In some cases, the two types of insulations are blended together throughout the sleeping bag. In others, the insulation may be in different locations, for example, durable synthetic on the bottom of a sleeping bag and lofty down on top.
- Lighter weight and more compressible than synthetic alone
- More water-resistant than down alone
- Less expensive than down alone
- Heavier and bulkier than down alone
- Less water-resistant than synthetic alone
- More expensive than synthetic alone
As you're considering your options, think about where you’ll be going, how much weight you want to carry, the weather you’re likely to encounter and how much money you’re aiming to spend. But, most importantly, once you find the right sleeping bag or insulated jacket for you, get out in the mountains and have some fun.
- Sleeping Bags for Camping: How to Choose
- Sleeping Bags for Backpacking: How to Choose
- The Best Down Jackets: Staff Picks
- How to Choose Insulated Outerwear
Editor’s note: REI has adopted the Responsible Down Standard (RDS) for 100% of REI Co-op brand products with virgin down and feathers. Many other leading outdoor brands have also adopted the RDS standard. To learn more about the RDS, refer to our Expert Advice article, Animal Welfare and Outdoor Gear.
In addition, the REI Product Impact Standards include the basic animal welfare expectation that apply to all brands selling products containing virgin down.
We invite you to read more about our other practices in our Stewardship Report.