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Down vs. Synthetic Insulation Guide

Posted by Erendira Garcia on

Deciding between natural insulation or the latest in synthetic tech depends on what you’re looking to get out of your jacket. We’re showing you the differences between them so you can decide what kind of insulation you’ll need for your winter adventures.

The Material

DownImagine, the fluffiest, softest, warmest blanket in the fanciest hotel room you can think of. That's down. Down is made up of the underplumage from the breasts and wings of geese or ducks. These are small, light bits of feathers (quill-free) that create tiny pockets of air that trap your body heat. It's the top of the line material for the best warmth.

SyntheticWhile there's nothing quite like Mother Nature’s natural insulation, many synthetic materials come really close! Most synthetic materials are long threads of polyester that are clumped together to mimic down clusters. They trap air (like down does) to keep you warm. Some common brands to look for include PrimaLoft and 3M's Thinsulate.


How to measure

DownThe fill number measures the volume of down per ounce. For example, one ounce of 700-fill down takes up 700 cubic inches. The higher the fill number, the more air (and heat!) is trapped. Most jackets will range between 350- to 700-fill, though some jackets go as high as 900-fill (though you probably won't need that unless you're climbing Everest).

SyntheticSynthetic insulation is measured in grams per square meter. These don’t measure the volume of insulation - instead, they measure how thick the insulation is. The general rule is that the thicker the insulation is, the warmer the jacket will be. So due to the power of math, 60g insulation will be warmer than 40g.



DownDown is light (you could say it's light as...a feather) and can be packed down very tightly. In fact, many sleeping bags and jackets come with a small pouch it can be stuffed into or it will even fit in a pocket that’s on the jacket itself. This makes down ideal for travel.

SyntheticSynthetic insulation is slightly heavier and bulkier than down, so if every ounce counts, you might not want to go with synthetic insulation. However, it can be a great option if you’re concerned about moisture, which leads us to...



DownWhen down gets wet, it clumps up and loses its loft, which means that those pockets of air trapping your body heat and keeping you warm are gone. It can also take a full day or more to fully dry. If your adventures are forecasting lots of rain, combo your down layer with a waterproof shell, or better yet, get yourself something synthetic!

Synthetic: This is where synthetic insulation shines. Fabric scientists (yes, that's a thing) know that it's hard to beat the warmth-to-weight ratio of down. But unlike down, synthetic polyester fibers don't collapse when wet, which means that they maintain their loft (and your body heat) even in a downpour. 




DownWe all love the feel and functionality of down but many people are concerned about how its obtained, since it comes from animals. We’re proud to report that many of the manufacturers we sell including Patagonia, The North Face, and Holden (coming soon!) source their down from ethical and responsible suppliers. Check out their pages for more information.


SyntheticSynthetic insulation is very ethical since it comes from the down of man-made robot ducks! Just kidding. But synthetic insulation has made it possible to create down-level warmth in a 100% ethical way. Materials like PrimaLoft's Eco series use high amounts post-consumer recycled plastic to create their insulation. 

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  • We are so impressed with how knowledgeable all of our customers are! We’re proud to be part of a community of people who love to share what they know. Your gear is more than just “stuff” which is why we always work hard to provide you with a variety of high-quality options that meet your standards.

    Erendira @ SB on

  • Time to add a comparison dimension: environmental impact. Sythetic fibers are now well demonstrated to degrade and persist in the environment, becoming so small (but intact) as to be absorbed into wildlife tissues. So, if the synthetic microfiber lofting is contained its ok, but if it’s exposed fleece that get washed a lot or the covering comes off, you may be contributing to plastic-ifying the environment.

    Sharyl Rabinovici on

  • Is there a down-synthetic corelation between weights of each and warmth, i.e., is 60gm of synthetic equal to 650 down fill?
    Good article. Thanks.

    Susie on

  • Thanks for the post! I wish that the manufacturers would stop putting toxic fluorinated DWR on insulating layers. There are perverse trade incentives that encourage this, but there’s no good reason to put toxic ingredients on insulating layers that will remain in our environment literally forever. I think if Basementeers knew that DWR is as bad as it is, they would prefer to reduce its use as much as possible and would ask manufacturers to not put it on anything but shells (and they should look for safer alternatives to fluorinated chemicals for shells, too!). Does SportsBasement do any advocacy on behalf of its customers? It would be great if retailers told manufacturers that we don’t need DWR on insulating layers and to stop it already. Thanks! =)

    Jen Jackson on

  • You’re missing something about Synthetic regarding the issue of Ethics. Truth of the matter is when we use, and especially when we wash all this synthetic clothing, tiny synthetic microfibers get into the water and environment, effecting the health of wild life through the food chain, including us.

    Sarah Stiles on

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