Guide to Down Fill – Here’s How Much You Really Need

When buying a down summer sleeping bag or a puffy jacket, you’ll need to decide on a lot of different features. From water-resistance to compressibility, your gear options are highly varied, so knowing what to look for as you shop is of the utmost importance.

However, in the world of down gear, there’s one technical spec that isn’t quite as easy to shop for; down fill power.

Down fill power is one of the most important metrics used in determining the quality of your down gear, but it also happens to be one of the most difficult to understand.

To help you figure out, once and for all, how much down fill you need, here’s our guide to determining what level of fill power is appropriate for your adventures.

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What is down fill power?

Fill power is essentially a measurement that represents how much loft in the down that’s used to make a jacket, sleeping bag, or pair of gloves.

Since loft is a fancy term for how fluffy down or synthetic insulation is, it helps us understand how good a garment is at actually insulating us. This is because down gear doesn’t actually produce heat to keep us warm. Rather, it uses its fluffiness to trap in our own body heat to insulate us from the cold.

So, fill power represents loft, which, in turn, represents a down object’s ability to keep you warm, per ounce of down fill. 

Higher fill power down has more loft, so that means it is better able to keep you warm than the same amount of lower fill down.

Down fill weight

However, it’s important to note that down fill power isn’t the end of the story. There are plenty of other metrics that are used to describe the quality of a down sleeping bag or jacket, such as down fill weight.

Down fill weight refers to the actual total quantity of down fill used to create a garment or piece of gear.

Remember how we said that fill power represents an object’s insulating abilities per ounce of down fill? 

There’s a reason that we added the per ounce qualifier there.

This is because fill power, on its own, can’t tell the whole story of down.

For example, if you have a high-quality 800 fill power down sleeping bag with a fill weight of 12oz (340g), it will be substantially warmer than a 400 fill power sleeping bag with a fill weight of 12oz (340g).

On the flip side, a 400 fill power sleeping bag with a fill weight of 12oz (340g) will be just as warm as a 800 fill bag with a 6oz (170g) fill weight. That’s because the manufacturers of the 400 fill bag made up for its lack of natural insulating ability by adding in more insulation. 

Sure, it’ll be much heavier and bulkier, but, all else being equal, it will likely be just as warm as the 800 fill alternative.

So, keep down fill weight in mind as we discuss what fill power of down you might need because these 2 metrics go hand in hand.

How much down fill do I need?

All this theoretical talk about down fill power is great, but it doesn’t necessarily do much for you when it comes time to actually buying gear

So, to ensure that you know what to look for as you shop, here’s some information on when certain fill powers of down are most appropriate.

800 to 1000+ fill down

800 to 100+ fill down is considered the cream of the crop in the world of down insulation. Downs with a fill power of 800 to about 900 are fairly common on the market today, though you’ll find only a handful of manufacturers that work with 950 to 1000+ fill downs because it’s so expensive and difficult to source.

Ounce for ounce, when compared with lower fill power downs, 800 to 1000+ fill garments and sleeping bags are the warmest, lightest, and most packable options on the market. They’re also, as you can imagine, the most expensive.

Note that we said ounce for ounce in our last statement. Referring back to our discussion of down fill weight, it’s important that you keep in mind the fill weight of any sleeping bag or garment you buy before you invest in an 800 to 1000+ fill down. 

If the fill weights of 2 garments are similar, the one with the higher fill power will almost always be the best quality.

Is 800 to 1000+ fill down right for me?

If you’re someone that heads out on light and fast backpacking trips or an alpinist that ventures into remote environments, 800 to 1000+ fill down garments, like the 800 fill Patagonia Down Sweater Hoodie, might be appropriate.

It’s particularly popular among folks who are hiking the Appalachian Trail or other long-distance hiking trails because of its excellent warmth-to-weight ratio. 800 to 1000+ fill down is also highly compressible, which makes it ideal for thru-hikers that carry smaller hiking backpacks.

But, above all, 800 to 1000+ fill down is expensive, like really expensive. Once you crest into the 900+ fill power range, you can expect to spend up to 2 times more on a jacket than you might with a 600 fill alternative.

So, 800 to 1000+ fill down is perhaps most appropriate for you if :

  • You need gear that’s very light or highly packable
  • You’re heading out on a long adventure in a remote locale
  • When it comes to quality, you’re willing to spend quite a bit more money

If these statements don’t resonate with you, then a different fill power of down might be more appropriate.

600 to 800 fill down

When it comes to down fill, 600 to 800 fill sleeping bags and jackets are a fantastic middle ground between expensive, high-end gear and budget-friendly equipment.

Ounce for ounce, a 600 to 800 fill power garment isn’t going to be as light or compressible as its 800 to 1000+ fill siblings, so you’ll often end up with slightly heavier gear. At the same time, however, 600 to 800 fill power gear has a much better warmth to weight ratio than 500 to 600 fill alternatives.

What really sets 600 to 800 fill gear, like the 700 fill Rab Microlite Alpine Down Jacket apart, is their value for the money. By sacrificing a bit in terms of weight and packability, you usually end up with quite large cost savings when you opt for gear with fill power in this range.

Is 600 to 800 fill down right for me?

While you might not end up with the lightest equipment on the market, 600 to 800 fill jackets and sleeping bags are perfect for the vast majority of outdoor pursuits.

In reality, unless you’re someone who really needs to cut a couple of ounces from their pack weight, you might not actually notice the difference between a 600 to 800 and an 800 to 1000+ fill power down. You will, however, notice the extra money in your bank account.

When deciding if 600 to 800 fill down is appropriate for your needs, ask yourself the following questions :

  • Am I okay with carrying a bit of extra weight and bulk in exchange for affordability?
  • Do I need gear that is light enough to take backpacking but isn’t overly expensive?

If you answered yes to both of these 2 questions, then 600 to 800 fill down is probably better for your needs than any of the other alternatives on the market. That’s because 600 to 800 fill down gear offers the perfect mix between performance and affordability.

500 to 600 fill down

Finally, we have 500 to 600 fill down sleeping bags and garments.

500 to 600 fill down is considered to be the most economical choice, so you’ll find it in a lot of budget-friendly gear. However, anything below 500 fill down is a bit too bulky for most outdoor applications, so you’ll really only see it used in duvets and pillows.

From our previous discussions on the connection between fill power and warmth to weight ratios, you can probably surmise that 500 to 600 fill gear isn’t the lightest or the most packable.

Indeed, while the 600 fill Patagonia Hi-Loft Down Hoodie is plenty comfy and warm, it’s really best for a car camping adventure to a mild climate, like Olympic National Park, than for a winter backpacking trip to Glacier National Park.

But, when it comes to keeping your overall costs as low as possible, it’s a solid choice.

Is 500 to 600 fill down right for me?

As we’ve mentioned 500 to 600 fill down is an ideal option for campers on a budget or for anyone that’s okay with using heavier and bulkier gear.

Not sure if it’s right for you?

Ask yourself the following questions before you decide :

  • Am I planning on car camping or doing very short backpacking trips?
  • Will I be using my gear in milder conditions, such as in the fall or spring?
  • Is affordability my chief concern?

If you answered yes to all of those questions, then 500 to 600 fill down might be right for you.

Alternatively, if you’d like gear that’s a bit more packable, it’s worth checking out 600 to 800 fill equipment, instead.

Gaby Pilson

Gaby is a professional mountain guide with a master’s degree in outdoor education. She works primarily in the polar regions as an expedition guide, though she can be found hiking, climbing, skiing, sailing, or paddling in some of the world’s most amazing places when not at work.