Down Jackets

Note: Down jackets are hard to deal with. I'd highly recommend synthetic insulated jackets instead. 

First thing you should know about down jackets is that you should only consider getting one for stationary use, in dry weather. 

Because, all down jackets offer: 

• Low breathability, 
• Poor wet weather performance, 
• Fragile outer shell.

Always. 

No exceptions. 

If this isn't you, then you should stop reading this post and go check out my Best Synthetic Insulated Jackets article. 

I'd also recommend you to check out my Best Arc'teryx Jackets and Best Patagonia Jackets articles. 

#Important note: A down jacket will lose its insulating capability under fairly wet conditions. Either from your sweat or wet weather. 

That's why, if you're going to be using them in damp areas, I'd urge you to consider getting a synthetic insulated jacket instead. They're mostly heavier, but perform better in wet conditions. 

Temperature Ratings

The warmth data provided below for each product are obtained either by: 

• Trying them out, 
• Analyzing them scientifically,
• And/or gathering tens of authentic, non-biased offline user experience.

As you see, there's a strong correlation between FP x FW and temperature ratings, but not more than, say, 80%. 

Let's clarify the reasons behind this. 

Warmth

Warmth is the most important thing you should focus on when getting a down jacket. There are two major factors to it: 

• Fill power, 
• Fill weight.

Note that these are major two factors, not only two factors. 

Fill Power

The word "down" is typically mostly referred to as "fill" in down insulated garment language. 

Fill Power refers to the fully expanded end volume of a 1 oz down (goose or duck). It's in cubic inches. 

For example, a 800 FP (fill power) down will end up getting as large as 800 cubic inches when it's fully expanded at rest. 

By the way... 

Fill power isn't only about warmth level at all. Having said that, all I'm currently trying to accomplish is to decode the nature of warmth in an analytical way. 

This is why I'm going to skip other roles of fill power and will get back to it later in this post. 

Here's a video that also does a good job explaining fill power: 

Moving on to our other major factor... 

Fill Weight

Fill weight is the amount of down the insulated piece is equipped with. It's just as important as fill power when it comes to warmth.  

Because, just like fill power, also fill weight directly affects the amount of air trapped within the vacant spots of down. 

That said, the role of fill power on other factors (long term warmth, warmth during movement, warmth distribution, compressibility) is significantly greater than fill weight. 

Important: Warmth Calculation

Reminder: Fill power and fill weight are the two most important factors when it comes to warmth. 

On a larger scale, assuming both jackets are equipped with identical synthetic insulation (or none of it), it is possible to make very close estimations by multiplying them when comparing warmth ratings of two different pieces. 

For example...

• Rab Neutrino Pro offers 227 grams of 800 FP down.
  • 227*800 = 181,600
• Outdoor Research Alpine Down offers 182 grams of 800 FP down. 
  • 182*800 = 145,600

Since 181,600 is significantly greater than 145,600; it's safe to say that the former will be warmer than the latter. 

Now...

There are reasons why this mostly won't work on a smaller (or sometimes even on a large) scale. 

The main reasons include but are not limited to: 

• Presence of other synthetic insulators,
• Length,
• Bagginess,
• Outer fabric,
• Fill power (I know this is confusing... ignore it for now).

Let's clarify them briefly. 

Synthetic Reinforcements

This is one of the primary reasons for this. For example, Arc'teryx always uses synthetic insulation strategically in high wear areas for all their down jackets. 

As you can guess, this is part of the reason why they're listed warmer than down jackets with equal FP * FW values. 

Length

In colder weather, it becomes much harder to keep your legs and feet warm than your torso and arms. 

This is why, the longer the hem length, the warmer the jacket will feel. And the difference is pretty noticeable. 

Bagginess

I talked about this more in detail in my Arc'teryx Thorsen vs Therme vs Camosun post. 

Briefly, the amount of trapped air increases as the jacket gets baggier. So more air works as insulation, and ultimately you're kept warmer. 

There certainly is something as "too baggy", though. After some point, more inner volume only holds the warmth back. 

Weather Resistance & Outer Fabric 

Outer fabric is actually much more about weather resistance, but it also affects warmth a little bit. 

As explained earlier, no down jacket is able to offer well weather resistance since they get clumped and loses their loft when they get wet. 

This is the case regardless from getting wet through your sweat or weather conditions. 

That being said, it's still possible to sort them by their strength. But the difference is minimal here - so much that it might not even be noticeable: 

Arato 30 = Perfex Quantum Pro > Perfex Quantum > Arato 10 = Drilite Loft 40D > Arato 7 = Drilite Loft 20D > others. 

Other impacts of Fill Power

Higher FP will retain its loft with minimal loss during movement. Whereas a lower quality (which is a lower FP) down will do a poor job with this. 

For the sake of simplicity and trying not to make this a scientific article, I decided to place equal importance (weight) on fill power and fill weight when calculating FP * FW values. 

But, in reality, I'd actually place more weight on fill power. Maybe squaring the FP and then multiplying it with FW would be a more accurate calculation to yield better results. 

How do down jackets compare to synthetic jackets?

Here's the full data set for Arc'teryx's and Patagonia's almost all insulated garments. 

Lastly, if you're interested in Patagonia only, check out my Best Patagonia Down Jackets post.