Fill Power and Fill Weight in Down Products

In this article I want to talk about down and when you’re purchasing a down product what to consider. What is down and why is it great? Also I want to talk about what is fill power versus fill weight.

What is Down?

There’s basically two types of insulation that you’re gonna find when you’re purchasing any kind of product. It’s either gonna be synthetic or down. There are other types, but they’re not in the majority by any means.

Synthetic is man-made, down is natural.

Some of the the pros for down is it’s super compressible and gives back its loft really well. It’s very warm, it’s a lot lighter than synthetic generally.

The biggest thing that most people will say about down (this is more of something that used to be said, I don’t think it’s as relevant now) but if down gets wet, it is not very good insulator. Actually it’s horrible because it clusters up and just it won’t keep you warm if it gets wet.

Synthetics will generally keep you warm if you get wet because they maintain their shape, they’re man-made.

But what’s actually happening and why down is so great?

heated winter jacket

The best natural insulator in the world is dead air space.

What’s actually happening in synthetics and down is that all the little fibers and the loft it gives is trapping dead air space. The same logic is behind why you get the the fiberglass pads in your house walls for insulation.

But when down gets wet, it clumps and is not giving you any loft and dead air space, which is why a synthetic might be better because they hold their shape and still give dead air space even when wet.

The reason I say I don’t think that’s as big a consideration anymore is because most recently the technology for hydrophobic downs has gotten really good. They treat the down before putting in the product so that it repels water and doesn’t absorb it. It doesn’t clump as much.

So I don’t see it as as big a consideration as it used to be even a decade ago.

That’s the pros and cons of a down.

See Electric Heated Winter Jackets

When you’re looking at a down product, you are basically looking at a few things. I’m gonna use the example of a jacket.

You’re looking at the total weight of the product, you’re looking at the compressibility of the product and you’re looking at the warmth of the product.

The warmth of the product is going to break down into two elements. It’s gonna be the fill power and it’s gonna be the fill weight.

Fill power is what you are going to see if you walk into an REI or look at an online store. Right off the bat, manufacturer is most likely going to tell you the fill power.

They’re generally going to be somewhere between 600 to 900.

battery heated jacket

The fill power is how many cubic inches of loft you get from one ounce of down.

For example, a 600 down jacket. It means is that one ounce of that fill will give them 600 cubic inches of loft in those little cylindrical test tubes that they use.

800 means that one ounce, the same amount, is going to give you 800 cubic inches of volume.

The difference there, if it’s the same actual weight of down, is that they’re using different types of down. For example, duck verse goose. Goose is the the premium.

But also the size of the individual down clusters. An 800 down cluster, the individual piece of down, is typically going to be closer to the size of a quarter, whereas a 600 may be around the size of a dime.

The type of down they are using is what differentiates the fill power.

Basically think of fill power as the quality of down that is being used. It does not mean that there is more down in one than the other. They are rating at the exact same thing. It’s just the type of down and the quality of the down, the size of the individual clusters.

What I used to think is that 800 meant that there was more down in it. It’s the same amount of down for greater loft. So fill weight is how much actual down they put into the product.

If the fill power is the quality, think of fill weight as the quantity.


In my opinion, I would say that the fill weight is actually more important of the two, but you need to take both into consideration. Both are important.

I think it’s on purpose that manufacturers push the fill power because most people don’t understand it.

For example, a light men’s parka down jacket could be 4.2 fill weight at 800 fill power. If you compare that to a really well known jacket with great warmth to rate ratios, super light, super compressible, and it’s also a 800 fill power, the first jacket is way warmer than that because it has more down in it.

The second jacket has 2.7 two eight ounces of filling. So it’s less down. They’re both the same, they’re both eight hundred, they’re both the same quality of down, but the first jacket has literally more down in it. This jacket is gonna be warmer.

See Battery Operated, Rechargeable Heated Jackets

Depending on what you’re looking for in a product, you want to consider both, but you could technically have a six hundred fill powered jacket that is warmer than an 800, if they put more down in it.

The point is that an 800 does not always mean it’s warmer than a 600 fill power. That’s the big misconception and that’s what I want to clear up in this article.

Fill power does not always mean warmer. You need to look at both. It’s the quality of the down. If I had to pick one over the other, I would look at how much down is actually in that product.

Also when looking at the weight, consider the material that it’s in. For example a jacket can be a 20 denier, which has a good combination of weight and durability.

But if you wear a seven denier jacket when rock climbing, I would be very concerned about it snagging. It’s durability is not gonna be as strong but it’s a lot lighter.

Depending on what you are looking for in a product, that’s where you balance what’s most important to you. Am I really just looking for something that’s really lightweight or am I looking for something that’s really warm. Am I going to Antarctica, in which case I should probably look at something that’s a fill weight of six or above.

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