Last Updated: October 9, 2020

Down Vs Synthetic Sleeping Bags

When you start getting serious about your choice of sleeping bag, you’ll soon realize there are tonnes of options out there, many of them carrying hefty price tags.

You want to make sure that your investment will be worth your while, and there are a range of factors to consider. The most important aspects will inevitably be warmth, weight, compressibility, maintenance and, of course, price.

Even if you’re fairly new to the world of sleeping bags, you’ve probably heard of down and synthetic insulation. They are both types of insulation used in sleeping bags, and each have their own pros and cons but, before we delve into those, let’s take a close look at what down and synthetic fillings actually are.

Down vs synthetic insulation sleeping bag

What is down insulation?

Down insulation is made from the super soft bird plumage that sits underneath the tough exterior feathers and the skin of the bird. It acts as a natural insulator for the bird itself, so it makes sense that it makes a great filling for warm sleeping bags.

How does down insulate?

Down itself is exceptionally light and fluffy, and it forms three-dimensional clusters. These clusters expand into air pockets, forcing the air from these pockets to sit in a series of smaller pockets within the cluster, via a process known as ‘lofting’. The air within the down structure becomes trapped, and any heat that escapes from the body will be held within the pockets rather than escaping, which is why it keeps you warm.

What is fill power?

When the down clusters are fully expanded, and trapping as much air as possible, they are said to be at maximum loft. The greater the quality of down, the greater its loft.

We use the term fill power when we want to compare the loft of down products. Fill power refers to how much space one ounce of down can fill, and the greater the fill power the greater the loft.

For instance, if down has a fill power of 600, that means that one ounce of the down will fill 600 cubic inches of space, whereas one ounce of a down with a fill power of 800 will fill 800 cubic inches of space.

The 800-fill down is filling more space and capturing more air (that is, it has a greater loft) and therefore has great insulating power than the 600-fill down.

What types of down insulation are there?

Traditionally, goose down has been used for insulation, but in recent years duck down has become more and more popular, mainly because of its lower cost.

A goose down with a fill power of 600 is no better at insulating than a duck down with a fill power of 600. However, because geese are larger than ducks, they have larger clusters of down. Therefore, these clusters can achieve a greater fill power than those from ducks, which means that top-range products tend to stick with goose down.

One thing to be wary of with down, as with all animal products, is the welfare of the animals used during production. In the past, geese used for down production have also been force-fed so that their oversized livers could be used for foie gras, a culinary delicacy renowned for its cruel method of production.

If you want to be sure that your down has been produced ethically, keep your eyes open for a seal of approval from the Responsible Down Standard or Global Traceable Down Standard, organizations that promote ethical down production.

Down vs synthetic insulation sleeping bag


The major selling point of down insulation is its fantastic weight-to-warmth ratio. It’s makes for incredibly lightweight sleeping bags – it does come from birds that need to fly, after all – but you can be sure that it will keep you warm too.

It’s also extremely compressible, which makes getting a down sleeping bag back into its stuff sack a lot easier than a synthetic bag.

The final advantage of down insulation is its lifespan – a high-quality down sleeping bag should last you a very long time, even with plenty of unpacking and packing.


However, there are some drawbacks too, the main one being that when down insulation gets wet it bunches together and loses loft, so it no longer keeps you warm. To counteract this somewhat, modern down sleeping bags are often treated with water-resistant coatings, but if your bag gets absolutely soaked you’ll still be in trouble.

On a similar note, down insulation requires special cleaning, and you definitely can’t pop a down sleeping bag in the washing machine after a trip.

Finally, the price tag on down sleeping bags is often much higher than those on synthetic bags

What is synthetic insulation?

Synthetic insulation is manufactured to insulate in the same was as down, but to continue insulating even if it gets wet (as we’ll see later – getting wet is a real issue with down).

When you’re shopping around, you’ll see tonnes of names for various synthetic insulations – lots of brands produce at least a few of their own – and this can make it extremely difficult to know what you’re really looking at. However, despite all the fancy names, synthetic filling is constructed from plastic strands, typically polyester, that are woven together to imitate down clusters.

What types of synthetic insulation are there?

There are two main forms of synthetic insulation – short-staple fibers and long continuous filaments. Although both forms try to create loft in a manner similar to down, there are some differences between the two.

Short staple fibers are, as the name suggests, short, thin fibers densely packed together to capture warm air. Their short length gives them some ‘wiggle room’, which means they feel flexible as well as soft and make for super snuggly sleeping bags. Importantly, this flexibility also means they can be compressed well, although it also makes them less durable than synthetics made from longer fibers and sometimes fibers bunch together creating cold pockets of air.

Long continuous fibers are, as the name suggests, longer than short-staple fibers and generally thicker too. The fact that they are made from continuous fibers reduces their flexibility, so they will feel stiffer than synthetics made from short fibers and they won’t compress as well. On the flip side, they will stay in place, which reduces cold spots, and they tend to have longer lifespans than other synthetic insulation.


The main advantage of synthetic insulation is its ability to retain some of its insulating properties even while wet. Obviously, we all try to keep our sleeping bags dry but, depending on your type of trip, this could end up being an important factor.

Similarly, most of them can handle being put in a washing machine (although we’d recommend using a cool wash), which can be super handy at the end of stinky trips.

As we mentioned previously, there are some organizations that promote ethical down production; however some people question whether this is ever really possible, and synthetic insulation avoids the issue of animal welfare altogether.

Synthetic sleeping bags are also generally a lot cheaper than their down counterparts, so if you’re looking to save some pennies, they might be a good idea.


The main disadvantage of synthetic bags is the lower warmth-to-weight ratio. You might get the same fill power as with down insulation, but the bag will weigh a lot more.

They aren’t as compressible as down sleeping bags either and getting them back into their compression sacks can be tricky.

Synthetic bags also don’t tend to last as long as down bags – the insulation generally gets less powerful the more it is packed and unpacked.

Do I want a down or a synthetic sleeping bag?

So, now you know how down and synthetic insulation works, and the pros and cons of each, but which one is right for your sleeping bag? Well, the answer depends on the kind of trips you’ll be taking.

If you’ll be backpacking in cold conditions, then you’ll probably appreciate the great warmth-to-weight ratio of a down sleeping bag – it’ll keep you warm and won’t weigh you down either. We’d also recommend a down bag if you think you’ll be taking regular camping trips because, although it won’t be cheap, it will last you a while. Plus, lots of the more expensive options come with warranties too for that added peace of mind over your investment.

However, if you think you’ll be doing more casual camping and you won’t be carrying your bag around on your back, then the weight probably isn’t so much of an issue. In that case, you may want to go for a synthetic sleeping bag. Even if you’ll be camping in cold weather, plenty of them have very low temperature ratings. Plus, you’ll save some pennies and can pop it in the washing machine as soon as you get home.

So for regular or backpacking campers, we’d recommend a down sleeping bag, but for more casual campers a synthetic bag is probably the way to go – enjoy!

About the Author Roger Timbrook

Roger is a little obsessed with travel. He has been to over 40 countries, broken 3 suitcases and owned over 10 backpacks in 12 months. What he doesn't know about travel, ain't worth knowing!

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