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Ask Me: How Can You Tell How Warm a Down Jacket Is?

Ask Me: How Can You Tell How Warm a Down Jacket Is?


With sleeping bags, we have temperature ratings. But with down/insulated/puffy jackets, what is best way to determine if a jacket will be warm or warmer or hot? Is it the amount of fill? Some but not all jackets indicate the amount of fill.



P.S. heading for Overland Track.

Feathered Friends Eos Down Jacket.
Testing the Feathered Friends Eos Down Jacket in Glacier National Park.

Hi Bruce,

You’re right, down and synthetic-insulation jackets don’t have ratings like sleeping bags (which, by the way, were not uniform for many years, though there is now a uniform bag-rating system; learn more in my “Pro Tips For Buying Sleeping Bags“). There is no precise measure of the warmth of down and synthetic puffy jackets, but there are ways to assess a jacket’s relative warmth before you even see it.

Down fill weight is one way to tell, though it’s not a measure of a jacket’s warmth—it’s only a measure of the total weight (in ounces or grams) of the down in the jacket. How much insulation is in the garment is obviously an important factor in warmth, but not the only one, because down comes in a range of quality ratings. And of course, PrimaLoft and other types of synthetic insulation have different weights and warmth-per-weight ratios.

Down fill rating (not to be confused with the down fill weight) is basically a quality metric, not an indicator of warmth. The fill rating refers to the volume, in cubic inches, that one ounce of that down fills; in other words, an ounce of 800-fill down will occupy 800 cubic inches of volume. Down feathers and other insulation keep you warm through trapping heat from your body in tiny air pockets within the insulation, so higher fill ratings translate to more warmth per ounce of down. Thus, if two jackets contain identical amounts of down feathers by weight, the jacket with the higher fill rating will very likely be warmer. But there are ultralight 800-fill jackets that obviously aren’t as warm as 700-fill jackets that have more ounces of down in them. You also pay more for higher fill ratings.

Get the right synthetic or down jacket to keep you warm. See my review of “The 10 Best Down Jackets.”

Arc’teryx Cerium LT Hoody.
Arc’teryx Cerium LT Hoody.

Consider the conditions in which you’ll use your puffy jacket. Standard down feathers lose their ability to trap heat once wet, making down insulation less practical in wet environments. Today, there are water-resistant (hydrophobic) treatments for down feathers that greatly improve the ability of those feathers to repel water, dry faster, and continue to trap heat when damp. A soaked synthetic jacket is still probably going to keep you warmer than a soaked puffy stuffed with hydrophobic down feathers.

In the real world, most of us rarely put ourselves in circumstances where our puffy jacket gets soaked; but consider that attribute of down and synthetic puffy jackets if you think there’s a possibility of facing that circumstance—or even a possibility of your puffy jacket getting damp and not having much opportunity to dry out. On a multi-day trip with rain or wet conditions every day, moisture from the air and your body can slowly accumulate in insulation, enough to cause down feathers to lose some loft.


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Mountain Hardwear Ghost Whisperer Down Jacket.
Mountain Hardwear Ghost Whisperer Down Jacket.

Similarly, while synthetic insulation traditionally was not as lightweight, compactible, and durable as down, some modern synthetic insulation materials, like PrimaLoft, have a warmth-to-weight ratio that competes with down, and are more packable and lightweight. They’re also constructed in a way that’s likely to make them more durable than older synthetics, although down likely retains the edge there: I owned one down sleeping bag (from Western Mountaineering) for about 25 years, using it on innumerable trips, and it did not noticeably lose any loft before I eventually sold it through a consignment shop (simply because I had replaced it with newer bags; I wouldn’t be surprised if someone’s still using that bag).

Having a hood certainly keeps you warmer and is worth the nominal additional weight and cost. I consider a hood mandatory in cold temperatures (near and below freezing), but less important on milder trips, when I may pack a hoodless, ultralight puffy jacket to reduce pack weight and because I’m bringing a light hat, anyway.


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Patagonia Micro Puff Hoody
The Patagonia Micro Puff Hoody.

The way in which a jacket is sewn matters. In short, so-called “sewn through” construction stitches the outer, shell fabric to the inner, liner fabric, creating pockets of down, but also creating cold spots at seams where there’s effectively no insulation. This method reduces a jacket’s weight and often its cost, and is practical in ultralight jackets made for cool but not cold temps (think: summer in the mountains). The more-expensive method of creating so-called box baffles eliminates those cold spots and makes a jacket look puffier, but adds weight and usually cost. Look for that type of construction in puffy jackets designed for temps near and below freezing.

Outdoor Research Refuge Hooded Jacket.
Outdoor Research Refuge Hooded Jacket.

With down jackets, I generally simplify it to the following standard, which applies to my body (I don’t get cold easily) and will apply differently to other people, depending on how easily they get cold:

•    For summer trips, when I’m trying to backpack ultralight and I expect temps no lower than the upper 30s or higher, I bring a down/puffy jacket weighing 8 to 10 or 11 oz. (total weight), and I supplement with my other layers or get in my bag when necessary.
•    For trips when the temp could dip below freezing, I want a jacket that’s 12 to about 16 oz.
•    For colder trips/winter, my jacket weighs 16 to around 20 or 22 oz.

I find occasional exceptions to that general rule, when a jacket is remarkably warm for its weight, usually because of the use of lighter materials, such as shell fabric, and construction methods that reduce weight.


Tell me what you think.

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See my review of “The 10 Best Down Jackets” and all of my reviews of puffy jackets at The Big Outside.

You might also be interested in my “Review: The Best Gloves for Winter,” which includes three-season gloves, my12 Pro Tips For Staying Warm Outdoors in Winter,” which offer products and tips that are also applicable to three-season backcountry trips, and my story “What Should I Wear? How to Dress For Outdoor Adventures.


I can help you plan the best backpacking, hiking, or family adventure of your life.

Got questions about hiking, backpacking, planning a family adventure, or any trip I’ve written about at The Big Outside? Email me at I’ll answer your questions to help ensure your trip is a success. See my Custom Trip Planning page for details.

—Michael Lanza


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About The Author

Michael Lanza

A former field editor and primary gear reviewer for Backpacker Magazine, Michael Lanza created The Big Outside to share stories and images from his many backpacking, hiking, and other outdoor adventures, as well as expert tips and gear reviews to help readers plan and pull off their own great adventures.


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    You so totally rock. I searched this question after a lengthy conversation with a retailer about how to tell which down jackets are warmer, short of buying a bunch and subsequently returning them (which is how I’ve generally had to do it in the past). Low and behold, your article popped up immediately, and I couldn’t have been happier when I saw your photo in the sidebar. I’ve been trying to compare down jackets online and was feeling a little frustrated until I found this; you answered all the questions I had. I knew your advice would be the best. Now that I’ve found your blog, I’ll be checking it often. Hope you and the family are doing well!!

    Pam Omohundro

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      Hey Pam, thanks and it made me smile to see your name pop up on a comment. I’m glad you found my blog. It was fun skiing with Luke and the boys again last winter. Hope your whole gang is doing well. Keep in touch! Comment on a story or drop me an email anytime I can answer a question for you.

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    How can I, if possible, estimate the comfort zone of a down sleeping quilt that’s been modified with more down?

    I bought a 850 FP grey goose down quilt to replace my down sleeping bag. This quilt is rated for 5°C. I then took a small goose down comforter and had the fill removed and placed in the quilt. I haven’t yet slept using the quilt outside as the temps here are still in the upper 30s to 40s.

    Is there a way to estimate its warmth value now that more down was added?

    • MichaelALanza

      Hi Jeffery,

      That’s a good question. The temperature rating of sleeping bags and quilts is set using a standardized method; see my “Pro Tips For Buying Sleeping Bags” ( for more explanation about that. Estimating a temperature rating without using that method would be like estimating the width of a doorway without using a measuring tape; you’re likely to be off by a bit.

      But the quilt’s warmth will depend on how much down you added to it, of course. You’d measure the weight of the down added and compare it against the amount of down the quilt had prior to modifying it (which is often available in manufacturer descriptions of a product online). You could also have measured the quilt’s total weight prior to and after modifying it, and subtract the weight of the quilt’s fabric from those numbers (calculate the fabric’s weight by subtracting the weight of the down in the original quilt from the quilt’s original total weight). Did you increase the amount of down by a fairly small fraction, or by as much as 50 percent, or by some other value? That would begin to give you an idea of how much warmth you added.

      A quilt’s warmth is also affected by its design, and the fact that it doesn’t seal up as completely as a sleeping bag. There’s a limit to its ability to trap body heat.

      My advice: If you had not used the quilt before modifying it, don’t make any assumptions about how warm it’ll be now; just experiment with it in temps around its original rating or slightly lower than its original rating. Have some warm clothes to wear to supplement the quilt when you start experimenting in temperatures that may test the limits of the quilt. How warmly you naturally sleep is another variable that can’t really be calculated.

      I hope that’s helpful. Good luck.


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Hi, I’m Michael Lanza, creator of The Big Outside and former Northwest Editor at Backpacker magazine. Click my photo to learn more about me and my blog. Click here to sign up for my FREE email newsletter. Join The Big Outside now to get full access to all of my blog’s stories. And click here to learn how I can help you plan your next trip.

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