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Are Down Jackets Warm? (Explained)

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Down jackets are on the market since 1936.

Meaning they are quite popular.

But, how warm are down jackets?

Here’s How Warm Are Down Jackets? (Scientific Explanation)

In short, you can pick up any down jacket and it is guaranteed that it will keep you warm in the winter season. However, the quality and amount of warmth will depend on the down fill power, fill weight, and jacket thickness itself.

When you’re doing your own research, you may noticed that some manufacturers label their jackets as 90% down and 10% feathers.

These numbers are not for the show because the higher the percentage of down in a jacket the warm it will be.

But what is down? Don’t mistake it with the feathers because feathers and down are two totally different things.

Feathers are just what you see in the exterior of the birds but the down is actually, the soft fluffy plumage underneath the feathers of goose or duck.

And this is the material that keeps both you and the birds warm.

Now, the down is naturally implanted in the bird’s body to keep them warm but if we want to use it we have to take a different approach.

A quick point: Mature birds produce more high quality down than the younger birds. Though down from mature birds are collected from seasonal molts of breeding stock while the younger one gets collected from the birds that are farmed for food (how cruel are we?).

Read Also: Can Leather Jackets do the Job of Keeping You Toasty Warm?

Understanding The Fill Power & Why It’s Important For The Down Jacket Warmth:

Before quilling down jacket, down fibers must be first made into clusters. These clusters contain thousands of fibers that are crisscrossing in every possible direction.

Here comes the role of fill power in a down jacket. Essentially fill power is a term that is used to measure the down loft which refers to the down fluffiness.

And, the warmth of the down comes from the process of lofting, where the down clusters are lofted or expanded to fill the space (measured in cubic inches).

Which result in the creation of a ‘trap for air’ meaning the air gets stored in these thousands of air pockets and started to act as an insulating layer only because it is receiving less convection.

The trapped air is also known as the still air and science says the air is the poor conductor of heat meaning in a down jacket this still air will reduce the heat conductivity.

Heat conductivity means, that it is a process by which the heat from your body tends to move toward the cooler side (in this case your surrounding) to make the equilibrium.

Which the down insulation resist and thus you remain warm even in freezing temperature.

Down is known to be the best natural insulation available in terms of warmth to weight ratio.

The ratio determines how much warmth you can get with a given weight of a down jacket.

This ratio depends on the fill power.

You may have heard of 600, 700, 800, and the 900 fill power down jacket.

Basically, the fill power starts from 300 and goes up to 900 and above. Though 900 is what is commercially available.

In easiest terms possible, 600 fill power means in its a maximum loft (when down clusters are fully expanded) an ounce or 28.34 grams of down will cover 600 cubic inches when put into the Plexiglas cylinder and compressing it slightly with a weight.

Similarly, the 900 fill power down will occupy the 900 cubic inches in its max loft.

Meaning the 900 fill power result in the bigger down cluster which helps them occupy 900 cubic inches of space. The bigger down cluster means it has more tiny air pockets to trap more air and thus it’s more insulating than lower fill power.

Any down jacket lower than 500 fill down is considered as low quality because of coming from the immature geese or duck which result in a smaller down cluster.

It does not mean that a higher fill power will weigh more because it is taking more space.

No, that’s the beauty of down, the higher fill power simply means that it will provide the same warmth in lesser weight and will be more compressible because of having high porosity or pores between the fibers.

Understanding Fill Weight (The Factor That Determines The Warmth Of A Down Jacket)

According to science, it is the fill weight that is more crucial to down jacket warmth than the fill power.

Because the fill weight means the amount of down put into the down jacket.

The fill weight of a down jacket measures in grams so the higher the grams of down in jacket the warmer it will be.

For example, the 850 down jacket will not be warmer than the 650 down jacket if the jacket has 100g of 650 down as compared to 60g of 850 fill down.

But here comes a twist.

Keeping the fill weight the same, the higher fill power down jacket will always be warmer than the lower down fill jacket.

Taking the same example, 100g of 850 fill down jacket will be a lot warmer than 100g of 650 fill jacket because as we saw 850 is higher than 650 so it has more number of insulating pockets.

And now, there is 100g of 850 fill down in jacket means it has a much higher number of insulating pockets to keep us warm.

Also, the 850 one will be a lot lighter than the 650.

Do Thickness Of Down Jacket Play Role:

Yes, the thicker the down jacket is the warmer it will be because the volume of down clusters has been increased which results in much slower heat conduction meaning much lesser heat loss as compared to the thinner down jacket.

As you’ll be amazed to know that most manufacturers don’t tell the Fill weight of their down jacket which plays a significant role in both warmth and jacket thickness.

Here we go with another tip, take a look at 600 and 800 fill power jackets and analyze the thickness of both jackets.

If the 600 fill down jacket is much thicker than the 800 one then go with 600 because it is going to keep you a lot warmer than the higher fill power. Though the weight is also increased as a side effect.

Because usually, the thicker the down jacket is the higher the fill will be. So the warmer it will be.

Types Of Down (Warmth Compared)

Down can be achieved from any bird that has soft feathers but in current days, all down jackets are either made up of the duck down or the geese down.

Are Duck Down Jackets Warm?

Yes, the duck down jackets are warm but the major problem with them is they don’t retain the loft for a long time because they have low fill power and generally smaller down clusters.

Are Goose Down Jackets Warm?

Goose down is the warmest down used in the jackets because of their large feather size and bigger down clusters they have higher fill power and thus provide the best possible insulation.

Are Down Jackets Warm When They are Wet?

No, down jackets won’t keep you warm if get wet because the down fibers are hydrophilic in nature meaning they can absorb water.

So, once they get wet all the fibers, clusters start to compress which forces the still air to escape in the surrounding.

As told, it is the trapped air between the down fibers which act as an insulating layer so that the body heat won’t find a way to conduct heat to its cooler surrounding.

Now if there is no trapped air, the heat conduction will increase, and gradually the body will be lost so you’ll begin to feel cooler because of the drop in the body’s temperature.

But still, there will be some trapped air so the down jacket will have 10% insulation according to the studies done.

In my opinion, 10% insulation will not be of much use when temperatures start to drop at a faster rate.

Are Down Jackets Warmer Than Wool?

Yes, down jackets are warmer than wool jackets because the down clusters hold heat better than the wool.

However, the main advantage that the wool has over the down is that it doesn’t lose insulation even when get’s wet because the wool fibers are water resistant that’s why they don’t get shrunk like down fibers which results in the departure of trapped air.

Are Down Jackets Warmer Than Polyester (Synthetic)?

Yes, down jackets are warmer than polyester or any other synthetic jacket because down clusters have thousands of insulating pockets as compared to polyester fiber clusters and have the highest warmth-to-weight ratio.

Due to a high number of air pockets, the down will be able to trap more still air in lesser weight and thus keep you warmer than synthetics.

However, polyester is water-resistant in nature so it will not lose its insulation as quickly as the down does when getting wet.

Are Down Coats Warm?

Yes, down coats are warmer because instead of the style there is not much difference between a down coat and a down jacket.

As explained, the down is the best natural insulation available due to its incredible ability to trap heat.

Though, please check out the fill power, weight, and thickness of the down coat because the quality and warmth of the down depend on these three factors.

Are Packable Down Jackets Warm?

It depends, the more packable a down jacket is the more fill power it has and the higher fill power denotes the higher warmth-to-weight ratio.

But, because the warm also depends on the thickness and fill weight.

Thus, if your packable down jacket has 900 fill power and is thicker (or more grams of down in it) than 700 fill power (it’s less packable) then I am 100% sure that your highly packable jacket will be a lot warmer than a less packable one providing the weight of both jackets is same.

Though, in general, a packable down jacket will be warm enough to wear on cold days.

Are Lightweight Down Jackets Warm?

Yes, lightweight down jackets are warm but they are not warmer than heavy down jackets that have more grams of down packed in it.

A lightweight down jacket means two things. Whether it has higher fill power or lower fill weight.

For example, an 80g 800 fill-down jacket will be more lightweight and warmer than an 80g 500 fill jacket.

Are Down Jackets The Warmest? (In Real Life)

In terms of warmth-to-weight ratio, the down jackets are the warmest but a synthetic jacket can be a lot warmer than a down jacket.

There is much synthetic insulation available that is giving comparable warmth like down.

Some examples are PrimaLoft, Thermoball, Thinsulate Featherless, Coreloft, PlumaFill, etc.

A down jacket will be the warmest as compared to synthetic if:

  • It has high fill power and fill weight.
  • If there are more number of grams of synthetic insulation as compared down then the synthetic one will be warmer than the down.
  • Synthetic insulation will also always be the warmest in wet condtions because they don’t loose the insuatlion like down does when get wet

What Temperature Should A Down Jacket Be?

It is purely a subjective question because it depends on lots of factors other than the down jacket itself.

Such as, are you a person who starts to run cold as soon as the outside temperature drops?

Or, are you someone who does do not have any problem with running cold? (I have seen people who don’t care about running cold, I am one of them)

Other factors, such as the wind chill, humidity, moisture content, sun rays temperature also affect the practical experience.

Are you planning to layer or down jacket or not?

So, all the above things play a vital role.

But on average, depending on the thickness, fill power, fill weight, down jackets with no too little layer can keep you warm from 60 to -20 degrees Fahrenheit.

Read Also: Patagonia Jackets Temperature Ratings? (Complete List)


I hope you got the answer that down jackets are warm but the degree of warmth varies from jacket to jacket. For example, a thicker and higher fill power and fill weight jacket can keep you warm even in freezing temperatures.

We also studied that, higher fill power does not always mean a warmer down jacket because if have lower fill power have a higher fill weight as compared to high fill power then the lower fill power jacket will be a lot warmer than the high fill power down jacket.

Because it’s all the science of using still air as an insulator and thickness to further reduce the heat conductivity.

He also discussed in much detail why a down jacket loses 90% of its insulation when getting we.

I wish this article will help you find the best down jacket for your need because it has everything that you need to know to buy a down jacket depending on how cold the outdoor temperature goes in your location.

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