A key decision when opting for new sleeping bags is whether to go with down or synthetic insulation.

Both will keep you warm, but each carries various costs and benefits. That means the decision will be unique to each person and may vary according to the: 

• Type of camping activities
• Environment
• Buyer’s economic considerations
• Buyer’s personal ethics 

Down: Nature’s insulation champion

Down comes from the soft, fluffy undercoating beneath the exterior feathers of ducks or geese. It’s nature’s original insulation system, allowing waterfowl to swim in frigid waters due to its ability to trap air and create warmth. 

The down in sleeping bags is made up of three dimensional clusters of feathers. They create numerous tiny air pockets, which trap body heat and create a warm microclimate around the body. 

Loft (or fluffiness) determines down’s quality. The greater the loft the more numerous and compact the air pockets, meaning greater heat for less weight (particularly important in backpacking scenarios.)

“Fill power” measures down’s loft. Larger numbers correspond to greater loft, meaning more numerous and more efficient air pockets. Fill power ranges from 300 to around 900, although it is more typical to see sleeping bags in the 500 to 800 range. An 800 fill sleeping bag is significantly warmer than a 500 fill bag of the same weight. 

Synthetic insulation: The engineered sleeping bag alternative

Manufacturers make synthetic insulation by using polyester fibers to create air pockets that mimic down’s heat trapping properties.

Synthetics solve some of the limitations of natural down, most notably down’s performance deficit when wet. 

Key differences

Performance

Down’s most celebrated performance characteristic is its warmth to weight ratio, an important consideration for backpackers and mountaineers counting every ounce. For example, an 800 fill down backpacking sleeping bag will weigh about 25 to 30 percent less than its standard synthetic counterpart. A 20 degree down sleeping bag can weigh a full pound less than a synthetic bag. 

While the weight savings is not as significant for mild weather bags, the difference becomes even more significant for winter sleeping bags. This performance advantage is often the most critical factor for backpackers and mountaineers, looking to avoid turning their adventures into an exhausting trudge. However, the advantage only holds up if the down bags are kept dry and properly maintained.

Water resistence

While down insulation is often more lightweight and packable than its synthetic counterparts, its Achilles’ heel is the performance loss when it gets wet or damp, whether from exposure to water while unfurled or when in its stuffsack. 

While it may seem counterintuitive since ducks and geese are waterfowl, those birds have a natural secretion system: They emit oil that gives a protective sheen to their feathers. In man-made products, water causes the air pockets to collapse, making them less-effective insulators.

In contrast, synthetic insulation uses polyester filaments designed to maintain their structure when wet. A synthetic sleeping bag will lose some of its insulative capability when wet, but will maintain a much higher percentage of its effectiveness when exposed to water. 

The choice between down and synthetic sleeping bags could come down to where you like to camp or backpack. Synthetic may be the better option If precipitation is a big factor, like in the Pacific Northwest or on the Appalachian Trail. But, if you camp in dry environments like the high desert or on California’s portion of the Pacific Crest Trail, down may serve better. 

Sleeping bag durability and maintenance

The durability and maintenance aspects of the two materials is a mixed bag. 

Down will last much longer (approximately a decade in many cases), but requires more meticulous care. Improper washing can destroy down’s loft permanently, so most manufacturers recommend professional washing or hand washing using special down detergents. 

Synthetic sleeping bags, on the other hand, are the workhorse material. Polyester fibers are more resilient and can be machine washed and dried without the same careful considerations. 

Finally, exterior shell management is paramount with down sleeping bags. Even small holes can create significant leakage of feathers, whereas synthetic fill tends to stay in place even when the exterior is compromised. 

For those ready to invest in maintenance, a down sleeping bag is ideal. Synthetic bags offer a more convenient, low-maintenance option. Both can withstand rough use, but down bags need immediate repair. 

Economic considerations

If you’re a beginner backpacker or mountaineer or trying to pinch pennies, synthetic bags can offer a more budget-friendly entry into the market. Down bags are considerably more expensive, and the prices rise in proportion to the quality of down. Eight-hundred fill power bags are considerably more expensive than 400 fill power bags.

Our recent analysis of the sleeping bag market demonstrated down bags command an average premium of $86 over synthetic options. However, down bags typically enjoy a life of 10 years or more with proper care, while synthetic bags need replacement about every 3 to 5 years, complicating the economic picture. 

Ethics and the environment

Troublesome down

Down is a contentious material. Traditional down collection involved plucking feathers from live ducks and geese. The industry has introduced new standards, specifically the Responsible Down Standard, which bans cruel practices like live-plucking. Brands who receive the certification must provide traceability throughout their supply chain, from the farm to the product. 

Efforts to use recycled down have gained ground recently. Products like comforters, pillows and discarded apparel can be re-used. Organizations like PETA and vegan groups maintain no down production can be considered humane, as the birds are often slaughtered for meat. 

Synthetic’s petroleum problem

Synthetic bags aren’t free from environmental concerns. Most synthetic fills are created from petroleum-based products, meaning each synthetic bag has a significant carbon footprint. 

Moreover, most of the bags are made of non-biogradeable materials, meaning that unlike their down counterparts, synthetic materials persist in the environment long after their usage ends.

Certain kinds of synthetic bags also use PFAS, or forever chemicals, which do not break down in the environment or the human body. These materials have been linked to various human health threats. Brands have made strides to develop PFAS-free alternatives. Furthermore, some synthetic bags are constructed of recycled materials. 

Further complicating the picture is the durability of down if properly maintained, meaning consumers could go through two or three synthetic bags during the lifecycle of a single down bag. 

Ultimately, the picture is complex and nuanced and the most environmentally responsible choice will come down to personal cost benefit considerations as well as individual use. 

Which sleeping bag is better?

There is no universally applicable answer to the question of down or synthetic bags. Individuals will make choices according to which environments they frequent and in which seasons and at which altitudes. Cost considerations will also prove a large factor as well as maintenance aptitude and willingness. Finally, a complex matrix of environmental factors will weigh in any decision, with some users placing greater weight on certain factors over others. The goal here at Gear Analytica is to help consumers make informed decisions. 

Check out our latest sleeping bag rankings, which maps which bags provide the greatest value by weighing material specifications against price and proven performance.