Have you ever noticed that sleeping bags come with a temperature rating that tells you exactly what conditions they're good for, but down jackets don’t?
If you’re a bit confused about this, you’re not alone.
Here at Alton, we get a LOT of questions from customers wanting to know how warm our down hiking jackets are, what their temperature rating is, and why we provide a temperature rating for our sleeping bags, but not our jackets.
So in today’s blog, we’re doing a deep dive on the surprisingly complicated topic of down jacket warmth.
By the end of this article, you’ll understand why some down jackets simply feel warmer and perform better than others (even when the specifications look similar on paper) and be able to choose a down jacket that is going to be warm enough for your needs.
Why don’t down jackets come with a temperature rating?
It might surprise you to learn that there is no standardised warmth rating system for down jackets like there is for sleeping bags (which use the EN/ISO testing protocol).
On the surface, down jackets and sleeping bags seem similar, right? So why would you get a standardised temperature rating for one product, but not the other?
Well, the short answer is that determining the warmth rating of a down jacket is way more complex than most people realise.
The long answer? Keep reading to find out.
Why do sleeping bags come with temperature ratings?
When you're in a sleeping bag, the way you use it is relatively easy to predict.
Think about it: you're always in a similar position (lying down), there’s one intended activity (sleeping), and the environment is usually controlled (you’re protected by some kind of shelter).
The outside temperature might be warmer or colder, but everything else is fairly predictable and consistent across all use scenarios.
In other words, the variables are controlled.
With controlled variables to work with, calculating the temperature rating just becomes a matter of plugging in the numbers into a mathematical equation.
This is why sleeping bag manufacturers can confidently say "This bag has a comfort rating of -5°C" and know it's going to be fairly accurate across different users and situations.
Why is temperature rating down jackets so complicated?
When you wear a down jacket, there are so many variables at play, and they are constantly changing.
Just think of the range of activities you might do in a down jacket.
Hiking through steep terrain, going for a stroll on a cold day, chilling at camp, skiing, photography, bird watching, fishing… The list is literally endless, and all of these activities require different energy outputs. Even from one moment to the next, your body heat can vary massively.
Then there’s the environmental variables, such as temperature, humidity, and the weather – wind, rain, snow, sunshine, shade. These all affect how your down jacket performs and how warm you feel as a result.
But the biggest, most unpredictable variable is YOU, the user.
Different people run at different temperatures. Things like metabolism, body composition, and hydration and nutrition influence how warm you feel. Two people can feel completely different in the same jacket, even if everything else is exactly the same.
Plus, what people wear underneath their down jackets changes from person to person. Someone wearing a down jacket over a merino thermal base layer and warm polar fleece will have a completely different experience from someone wearing it over a light cotton shirt.
This mind-boggling range of variables makes it nearly impossible to say "this jacket will keep you warm in -10°C" with the same certainty as a sleeping bag rating.
Why down jacket temperature ratings aren’t that useful in real life:
The only way to truly determine a down jacket’s temperature rating is by controlling the variables we mentioned before, just like sleeping bag manufacturers do using the EN/ISO testing protocol.
Here’s how you’d do it:
First, you’d get a test dummy heated to exactly 37°C to mimic human body temperature.
Then you’d put a ‘standard’ base layer on, such as a mid-weight merino thermal, and some ‘standard’ pants on the lower body, such as thermals and soft-shell trousers.
That done, you’d put the down jacket you’re testing on the dummy, making sure the hood is up (if it has one) and all zip are closed.
Finally, you put the dummy in a climate controlled room and expose it to lower and lower temperatures while measuring heat loss until you get to the ‘critical’ point where a human would begin to suffer from hypothermia (body temperature drops under 35ºC).
The end result? A precise temperature rating for a down jacket being worn by a motionless human-shaped heater in controlled laboratory conditions.
And that, my friend, would be scientifically accurate and practically useless.
We can’t speak for you, but we personally have never met anyone who wanted to buy a down jacket so they can stand perfectly still in a cold room for hours on end.
But hey, maybe that’s your thing.
So how can you tell how warm a down jacket will be?
Even though temperature ratings don’t tell you much about how warm a down jacket will be, there are some other important factors that you should look for when choosing a down jacket. These are:
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Fill power (loft)
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Total fill weight
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Hydrophobic down treatments
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Shell material
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Baffle construction
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Length & other features
Let’s go through these one by one.
Fill Power (Loft)
Down fill power, also called loft, refers to a scientific measurement that tells us how much air is trapped in the down clusters. Down insulates by trapping air pockets between its filaments. The more air it can trap, the better it insulates. Higher fill power down has larger, stronger clusters that can trap more air in less space.
But it’s important to remember that fill power is a measure of down quality and efficiency, not absolute warmth. That’s why an 800 fill power down jacket can provide the same warmth as a 600 fill power down jacket while using less down and being lighter.
However, higher fill power down takes longer to produce, so it is more expensive and is often used in premium, high-performance down products that need to be ultra-warm and ultralight.
Fill power ranges at a glance:
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550-650: Entry-level, adequate for mild conditions.
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700-800: High-quality, good balance of warmth and compressibility.
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850-900+: Premium quality, extreme warmth-to-weight ratio.
Total Fill Weight
Fill weight refers to the total amount of down insulation in the jacket. While fill power tells us about down quality, fill weight tells us about the down quantity.
However, a lot of manufacturers don’t include fill weight in the specs of their down jacket because it varies so between sizes. For example, the same down jacket will have very different fill weights when it’s in size extra-small compared to extra-large, but they’d still have the same warmth rating.
If fill weight is provided, it can be helpful in comparing between specific down jacket models – but to make any kind of meaningful comparison, you’ll need to be sure that you’re looking at the fill weights for the same size jacket.
Hydrophobic Down Treatments
Down's biggest weakness has always been that it loses the ability to provide insulation when wet, but hydrophobic down treatments have been developed to combat this problem.
Hydrophobic down treatments like DownTek™ PCF-Free work by creating a protective, water-repellent shield over the individual down clusters. This doesn’t directly increase a jacket's warmth rating in dry conditions, but it can dramatically improve performance in real-world scenarios.
Treated down also dries out again much faster after it is exposed to moisture, whether that’s rain, sweat or humidity, making it more practical for a wide range of situations and uses.
Effectiveness varies between manufacturers and specific technologies, but in general, treated down will provide far more reliable warmth and insulation compared to untreated down.
Jacket Shell Material
Most technical down jackets for hiking and other outdoor activities use tightly-woven nylon or polyester that are engineered to achieve a balance between wind resistance and breathability based on the jacket's intended use.
Some manufacturers will mention the denier of the shell fabric in their product specifications, such as 10D or 30D. Denier represents the thickness of individual fibers in a fabric, with lower numbers indicating finer threads.
Generally speaking, the higher the denier, the more durable, thick and heavy the fabric will be. Many down jackets these days are made with ultralight, low denier (20D or less) fabrics to save weight, but this often means they aren’t suited to hard use in rugged environments.
Baffle Construction
In a nutshell, a baffle is a compartment within the jacket that holds down insulation in place. Think of it like individual chambers that keep the down clusters from shifting or clumping up in one area. Without baffles, all the down would simply fall to the bottom of your jacket.
The most common baffle construction method is stitch-through baffles, where the outer and inner fabrics are sewn directly together to create chambers for the down.
Down jackets with stitch-through baffles tend to be lighter, more packable, and less expensive. However, this method can lead to cold spots. For mild conditions or active use scenarios, this might not matter. But if you're camping in freezing winter conditions with low physical activity, you'll feel those cold spots.
Box-wall baffles are another common construction method used in down jackets for hiking and other outdoor activities. Box-wall baffles create three-dimensional chambers that allow the down to provide optimal loft with less chance of cold spots forming.
But although down jackets with box-wall baffles are slightly more effective at trapping heat, they're typically a little bit bulkier and more expensive. Box wall construction is great if you are planning to use your down jacket for static scenarios like fishing, photography or belaying in cold weather conditions.
Some down jacket manufacturers are switching to modern construction techniques such as welded baffles or bonded baffles. These methods eliminate stitch holes that can leak down and create cold spots. Welded baffles can also provide better weather resistance since there are fewer places for water to seep in.
Length & Other Features
The design of your down jacket isn’t just about how it looks – every design choice and feature makes a difference to the warmth.
The longer your down jacket is, the more of your body it covers, and the warmer you’ll be. For medium to high-intensity uses, such as hiking and backpacking, you want a down jacket that’s lightweight, packable and warm but not restrictive. In this kind of scenario, a hip-length or waist-length down jacket will be ideal.
For low-intensity scenarios, such as fishing, bird-watching, or photography, where weight and packability is not the priority, then you might want something longer that covers your butt and some of your legs, too.
Another feature worth mentioning is a hood. For cold-weather activities like winter hiking, camping, or just standing around in chilly conditions, a hood can make a big difference to your overall warmth. Down jackets without hoods are suited to more active situations, or when used as part of a layering system in variable conditions. Hoodless down jackets typically have a high-neck collar to help seal in the warm.
Cuffs, hem and collars are also important because they prevent warm air from escaping. Other features like internal draft buffers and snap closures over zippers help stop wind from penetrating through zipper teeth. These are all small details in the scheme of things but they do make a difference in extreme conditions.
How are down jackets rated for warmth, if they don’t have a temperature rating?
Some down jackets come with a warmth recommendation for certain activities, weather conditions, or seasons based on all the factors mentioned above.
This might not be as ‘precise’ as a laboratory test, but it does provide much more valuable information about how the jacket will actually perform when you're out there using it.
While different manufacturers have different terms to express this, most down jackets typically fall into one of four warmth categories:
Lightweight Down Jackets - Cool Conditions
Conditions: Cool conditions
Approx. Temperature Range: +15ºC to 0ºC
Best for: Warm mid-layer for cool to cold weather, or the warmest layer in mild climates.
Lightweight down jackets prioritise packability and mobility over warmth, making them perfect for active scenarios in cool conditions. They tend to have under 150g of down fill with a fill power ranging from anywhere from 600 to 800.
Generally speaking, lightweight down jackets can be comfortable in temperatures as low as 0°C when moving vigorously, but if you’re standing still they may only be suitable for temperatures above 15ºC.
Lightweight down jackets are designed to work as a part of a layering system, so you can add or subtract layers to achieve the perfect level of warmth. They often feature a slim fit that can be worn under other layers without adding too much bulk.
Lightweight down jackets are frequently made with high loft goose down that is extremely compressible for easy packing, as well as ultralight shell fabrics (usually around 10D). However, these ultralight materials can be more susceptible to damage.
Midweight Down Jackets - Cold Conditions
Conditions: Cold conditions
Approx. Temperature Range: +5ºC to -10º
Best for: Warm layer for all-round use in cold weather
Midweight down jackets, like our men's and women's Tough Down Jacket, are the perfect warm mid-layer, suitable for general-purpose use in most cold conditions.
They’re generally warm enough to be used as your warmest layer in active scenarios in temperatures down to -10°C, or as a mid-layer for light activity in freezing temperatures around 0ºC. However, if you’re just standing around, then they might only be warm enough for temperatures down to about 5ºC, but it really depends on what other warm layers you’re wearing.
Midweight down jackets usually contain 150-250g of down, although this varies a lot depending on the fill power of the down. Remember, the higher the fill power (loft), the warmer it is, so a goose down jacket with a high fill power (750FP or more) will require less down to achieve the same warmth as a down jacket with a lower fill power.
Heavy-Weight Down Jackets - Very Cold Conditions
Conditions: Very cold conditions
Approx. Temperature Range: 0ºC to -20º
Best for: Ultra-warm mid-layer for cold to very cold weather
Heavy-weight down jackets take us into serious winter territory, designed to be your warmest layer in temperatures down to -20°C during light to moderate activity.
These jackets are often made for specialised activities such as mountaineering, ice climbing, and hiking and camping in high-elevation areas. However, they’re also perfect for stationary activities in lower elevations where you aren’t generating much body heat.
Heavy-weight down jackets contain anywhere from 250g to 350g of down fill and often use higher fill power down (750-900FP) to maximise warmth without adding too much bulk and weight. The downsides of this are that they’re often quite expensive and can be way too warm for active scenarios in lower elevations.
Expedition Down Jackets - Extreme Conditions
Conditions: Extreme conditions
Approx. Temperature Range: below -20ºC
Best for: Warmest layer for highly specialised scenarios in extreme winter weather
At the extreme end of the spectrum, expedition down jackets are built for survival in the harshest conditions on Earth, handling temperatures below -20°C during light activity.
These jackets are built for serious cold and typically contain more than 400g of the highest quality down (800-950 FP). This means they’re overkill for most users – not to mention extremely expensive, heavy, and bulky.
Expedition down jackets are made specifically for extreme conditions. They use the toughest materials, often feature expedition-specific details, and are usually longer and more generous to accommodate multiple heavy layers underneath.
Expedition-grade down jackets are essential for polar expeditions, high-altitude mountaineering, and extended winter camping trips in extreme environments such as the arctic. They're also used in scientific field work in the world's coldest regions.
How warm should YOUR down jacket be?
The best down jacket is the one that matches your specific activities and needs. Maybe that looks like a versatile midweight down jacket that offers a good balance of warmth and versatility.
But if your activities fall clearly into high-intensity or low-intensity categories, don't compromise - get the specialised jacket that will actually serve your needs.
Simply put, the perfect down jacket isn't the one that provides the most warmth. It's the one that provides the right amount of warmth for what you're actually doing.
So rather than worrying about the exact temperature rating, focus on finding a down jacket that fits your needs and makes you feel confident in the conditions you'll face.
To do this, take some time to think about your specific needs:
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What activities will you be doing?
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What’s the typical temperature range you’ll be in?
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What kind of weather conditions will you be facing?
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How much do you personally feel the cold?
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What do you want out of a down jacket?
Remember, a good down jacket will usually work for multiple activities, but focusing on your intended use scenarios will help you understand what you need from your down jacket – and how to use it to best effect.
Want to know how to choose the best down jacket for you?
This blog is just the tip of the iceberg when it comes to down jackets, but at least now you understand why down jackets don't come with standardised temperature ratings like sleeping bags do, right?
