jackets temperature ratings

Summary

Most companies will claim that providing temperature ratings isn't possible.

And they're not incorrect. There are tons of fluid parameters that are difficult to measure if not impossible. Not to even mention the subjective nature of the feeling of warmth. 

Having said that... 

It is possible to provide approximate values for an average person making some strict assumptions around layering and weather conditions. 

Which is what you'll find out in this post. 

The context of this study will be evaluated in two parts: 

• Working principles of down jackets, 
• Working principles of synthetic insulated jackets. 

Let's get to it. 

Understanding the Working Principle of Down Insulated Jackets

Down quality and down amount are the two most important things when it comes to the ultimate warmth provided by any down insulated garment. 

You'll mostly come across this as fill power and fill weight respectively. 

Because the word "down" is typically referred to as "fill" within the language of down pieces. 

Let's take a look at the former first. 

Fill Power

Fill Power represents 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 800 cubic inches when it's fully expanded. 

This number varies anywhere from 500 to 1000, although the majority of quality brands (such as Arc'teryx, Patagonia, Feathered Friends, Outdoor Research, Marmot, REI Co-op, Enlightened Equipment, Rab, Black Diamond, Mountain Equipment and Mountain Hardwear)...

...mostly use down between 650 FP and 850 FP. 

As you'll see, there are outliers, though. A notable one would be Feathered Friends Eos, which is equipped with a whooping 900 FP down. 

Now before we get to fill weight, speaking of fill power...

...warmth actually isn't the only thing that it affects. 

Other roles of fill power

It has additional three important roles: 

• Loft retention during movement: Higher FP down will retain its loft with minimal loss during movement. The lower the FP, the larger the loss in this department. 
• Higher impact on end warmth: Compared to FW (fill weight), FP has a larger impact on the warmth the insulated jacket provides. 

• Durability of insulation capability 
  • A jacket with a higher FP down minimizes its loss of insulating power over time. You'd be able to use a 850 FP down jacket for decades, and it'd feel almost just as warm as the first day you put it on. 
  • A jacket with a lower FP down, on the other hand, might not and probably will not prove nearly as durable. In our experiences, jackets equipped with 650 FP down are more likely to feel noticeably colder after, say, 2-3 years. 

• Compressibility: A jacket with a higher FP down will offer a smaller packed size. 

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 total amount of down the jacket is equipped with. 

Some other resources might claim that fill weight is much less important than fill power when it comes to warmth, but that's far from reality.

In terms of warmth, fill weight is very, very important. Almost (in some conditions it even is) just as important as fill power. 

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

Warmth Calculation

So... 

As explained earlier, fill power and fill weight are the two most important factors when it comes to warmth. 

In many cases, on a larger scale, assuming both jackets are equipped with the same amount of equally capable synthetic insulation, it is possible to make very close estimations by multiplying them when comparing warmth ratings of two different pieces. 

For example...

• Arc'teryx Cerium SV offers 162 grams of 850 FP down. 
  • 105*900 = 137,700
• Rab Positron Pro offers 300 grams of 800 FP down. 
  • 116*650 = 240,000

Since 240,000 is significantly greater than 137,700; it's safe to say that the former will be noticeably warmer than the latter. 

One point should be made in here is that although the Positron will come warmer, thanks to the higher FP down of Cerium SV: 

• it'll stay almost equally warm even after decades, 
• it won't lose its insulation during movement, 
• and it's quite a bit compressible. 

Now... 

There are reasons why this mostly won't work on a smaller scale (more on these later, under Other Factors heading). 

Understanding the Working Principle of Synthetic Insulated Jackets

Synthetic insulated jackets imitate the working principle of down insulated jackets. They're equipped with artificial insulators, rather than natural down obtained by geese and ducks.

Some examples to the names of these artificial insulators can be given as Coreloft and PlumaFill. Comparing the temperature ratings of synthetic insulated jackets is more difficult. 

Because, unlike fill power parameter in down jackets, there isn't a common denominator to compare different types of synthetic insulators in an analytical way. 

Maybe except one parameter? 

CLO values

CLO value is the insulation power of an insulation setting.

For example, this value is 0.92 for 1 oz (28.35 grams) of a dry PrimaLoft One for one square yard. The important thing here is that unlike fill power, CLO is not a characteristic that is unique to one ounce of the material.

As you see in the example above, it isn't independent from the area of insulation (square yards). 

So, a higher CLO actually points out to the insulation capability of an insulation setting as a whole. It does NOT necessarily mean that the insulator being used is any more capable than an insulation setting put together with a weaker insulator. 

Given the right amount of thickness, any insulator can achieve desired CLO value. It's just going to end up being heavier. So, metaphorically, you can think of CLO value in synthetic insulated jackets as FP * FW value in down insulated jackets. 

• Read more about CLO values: https://outdoorcrunch.com/clo-values/ 

Unfortunately, obtaining the CLO value for commercial products is absolutely impossible. 

Having said that... 

We can (and we do) use a made-up parameter to CLO/oz/yd² to replicate FP in down jackets. 

But unfortunately, a new problem arises here. A fair amount of manufacturers come up with their unique insulators - such as Coreloft, PlumaFill, Octa, Stratus, FullRange, etc. 

And just like CLO values, they're unwilling to reveal the CLO/oz/yd² values of their insulators too. Which are the numbers we would need to determine the warmth. 

I asked Arc'teryx and Patagonia Customer Services myself about this, and came back empty handed. 

Having said that... 

During my research, I did come across some useful information that I can leverage. For example, as it turns out, the CLO/oz/yd² value for PrimaLoft One is 0.92. It's also 0.79 for PrimaLoft Sport and 0.74 for PrimaLoft Eco. 

However... 

These values aren't certain or completely trustworthy by any means. They aren't the results of scientific studies. I didn't detect them in any other place rather than forums, Reddit, or contacting manufacturers myself. 

In the end, I put what I could find together and did my best to make an estimation. Fortunately, this calculation using the numerical value CLO was not the only information I had in my hands. 

I had two additional (at least equally helpful) data: trying them out myself when I could, and gathering offline user experience. 

Warmth Evaluation

So, in the end, I used at least two of these three items to estimate the overall temperature rating of an insulated jacket: 

• Analyzed them scientifically (as explained earlier), 
• Trying them out myself when I can, 
• And/or gathering offline user experience. 

And mostly all three above. 

In addition to insulation types and amounts (which is what I covered so far), there are also other factors that impact the warmth of an insulated jacket. 

Other factors

Let's talk about the most important and most common examples of these factors.

In most cases, these are considered minor next to insulation specific qualities. But they do have a noticeable effect, and combined together, they might come close to affect the warmth as much as the insulator capability and amount. 

• Bagginess,
• Length,
• Outer fabric,
• Distribution of insulation. 

Bagginess

I also talked about this more in my 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. 

Length

This has two effects.

First one is that the amount of trapped air, which is explained above.

And second, in colder weather, it becomes much harder to warm your legs and feet than your torso and arms. 

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

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 top notch weather resistance since they get clumped and lose their loft when they get wet. Either from your sweat or from weather conditions. Doesn't matter. 

Having said that, it's still possible to prevent it to a certain degree. Some products offer a more fragile face fabric, while others can bead water more efficiently. These are directly proportional to face quality and DWR coating. 

For face fabrics, I'd list them like this: 

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

For synthetic jackets, outer fabric affects the warmth noticeably less. 

Fill distribution

Some products of my favorite brand Arc'teryx are guilty of this. Take Firebee AR (read my review), for example. Nothing is wrong with the insulation at the back, collar and torso. They feel perfectly warm. 

Whereas the insulation in arms, especially in lower arms, are seemingly slightly inadequate, which in the end affects the warmth feeling a little bit. 

Reinforcements

Some (most?) down jackets are reinforced with synthetic insulation in strategical locations. More often than not, these are high wear areas such as shoulders, back, elbows, etc.

For the sake of simplicity, I don't list them in my tables - although I do take them into consideration when evaluating the end warmth of a jacket. 

This is why you can see a jacket with smaller FP x FW rating outscoring a jacket with higher FP x FW rating. Because the former is equipped with (more) synthetic insulation reinforcements. 

Results: Temperature Ratings

Down jackets lose insulating power noticeably when it gets wet. Synthetic jackets don't. This is why the dry weather assumption was made for both of them.