Synthetic Insulation vs. Down
Do I want a warm jacket with goose down or synthetic insulation? Your answer will mostly depend on your intended use. Good quality down is warmer for its weight than any synthetic insulation and much more compressible. However, down's weak point is a complete loss of loft (and therefore warmth) when it gets wet. Insulation made of synthetic fibers maintains much of its insulating ability when wet, continues to keep you warm, and dries much more quickly.
Good quality down will maintain its loft and warmth over time better than synthetic insulation. Though it's a pain to wash, dry, and fluff up, goose down can withstand decades of being stuffed in your pack. In addition to being less compressible than down, synthetic insulation will eventually lose its ability to fully rebound from being compressed, meaning that it won't be as warm. The synthetic fiber matrix just isn't as durable as Mother Nature's goose down. Insulated jackets are significantly more user-friendly though - just throw 'em in the washer and dryer when they need a wash.
Synthetic insulation is the obvious choice for jackets used as a mid-layer under a shell. Even the most breathable shells create a more humid environment next to your body than outside and your mid-layers should both retain their insulating properties when damp with sweat and be quick and simple to dry. Not only does down lose its loft very easily when damp, it also loses loft (and thus warmth) when squished between a hardshell and your body. This is another reason to opt for synthetic over down. Additionally, synthetic insulation's ability to dry quickly, because the fibers themselves haven't absorbed water, makes all the difference. A half hour in the sunshine will often completely dry a soggy synthetic jacket like the Patagonia Nano Puff Hoody or The North Face ThermoBall Hoody, while a goose down jacket will remain damp and lumpy.
For warmer jackets used as an outer layer, down and synthetics have compelling advantages for different environments. For use in cold, dry environs, the warmth-to-weight advantage of down is a good choice. In wet, cold climates, like the Cascade Mountains or Alaska, a big burly parka like the Patagonia DAS Parka is a safer choice. Synthetic insulated outer layers are popular for any extended activity where you might get wet from snow or ice melt.
Innovations in both synthetic and down insulation are making their way onto the market this year. Each of these innovations attempts to capture the advantages of the competing insulation. The North Face's ThermoBall synthetic insulation mimics goose down's loose structure, creating more warmth for its weight than traditional synthetic batts. We are excited to follow this evolution as more manufacturers experiment with synthetic fibers that imitate the structural geometry of goose down. On the other end of the spectrum, manufacturers have also been experimenting with increasing goose down's resistance to water. This is certainly the long sought-after holy grail of down technology. Patagonia, Mountain Hardwear, and Rab have introduced down coats with hydrophobic down, meaning that the feathers have been treated to make them resistant to water. Down's inability to perform when damp or wet is its primary disadvantage and improving its water resistance would be a game-changing development. The jury is still out on how effective these treatments are performance-wise.
Synthetic vs. Down vs. Fleece
Let's take a minute and make the case for choosing synthetic insulation over down. Generally speaking, down is much warmer for its weight than synthetic insulation. In terms of offering weight-efficient warmth, synthetics have yet to match mother nature, though the gap is closing. Down however, has one major drawback - it is vulnerable to moisture.
When used as a mid-layer under a shell, a jacket with synthetic insulation will not lose its warmth by accumulating sweat like down is prone to do. When used as an outer layer, insulated jackets also have extended functionality in snow or light rain. Additionally, they are often more affordable than down, which makes them a great value. Fleece jackets or pullovers also serve as both mid-layers and outer layers. Although synthetic is warmer for its weight than fleece and offers better weather protection when used as an outer layer, fleece is more breathable and much cozier. Check out our Buying Advice article for an in-depth comparison of down and synthetic insulation, including breathable synthetics and information about hydrophobic treatments for down.
Types of Synthetic Insulation
The jackets we tested in this review utilize no fewer than seven types of synthetic insulating fibers. These fibers are mainly polyester - some are super thin and some relatively thicker. Combining multiple thicknesses and lengths of fiber in varying percentages is a popular strategy. Most of these options utilize many short fibers added together to form a dense mat. These dense mats, or batts, are then sandwiched between outer and inner fabrics. To keep the insulation in place, it is either sewn to the outer fabric or the inner fabric, and sometimes both.
What do those weights mean?
Comparing the loft and resultant warmth of synthetic insulation can be quite difficult. Our real world testing in cool to cold conditions proved that some types of insulation, like Primaloft Gold and Fullrange, are warmer than others in practice. The grams per square meter measurement simply states the weight of the insulation used (irrespective of loft and warmth). For example, we found that 60 g/m2 PrimaLoft Gold delivers more loft and warmth than 60 g/m2 Arc'teryx's Coreloft.
Standard Synthetic Insulation
PrimaLoft is the most common synthetic insulation used among the products in our review. Developed in the mid-80s in response to the US military's request for a down alternative that would remain warm when wet, its varieties continue to expand and improve.
Primaloft Gold is widely considered to be the industry best when it comes to synthetic insulation and the standard in terms of warmth-to-weight ratio. Previously known as PrimaLoft ONE, it is made with extremely thin individual fibers and provides insulation by capturing body heat in the countless tiny air pockets that exist between these fibers. The thinness of the fibers allows not only for more trapped air in a given amount of insulation, but also allows for relatively good compressibility.
Primaloft Silver Hi-Loft, seen in the Patagonia DAS Parka, is a continuous filament insulation made with fibers of differing thicknesses. Primaloft calls this their loftiest insulation. This insulation is less compressible overall, but more durable in the long run.
Coreloft, Arc'teryx's proprietary insulation, is made of many short, thin fibers, and is used in the Arc'teryx Atom LT and Arc'teryx Atom SL It is very warm, but not quite as warm as PrimaLoft Gold.
Breathable Synthetic Insulation
FullRange Insulation, developed by Japan's Toray Mills and Patagonia is used in the innovative Patagonia Nano-Air Hoody. It also uses a combination of thicker and thinner fibers. The secret additive in this mix - a trade secret - is claimed to both stabilize the fiber matrix and allow more stretch and breathability than Primaloft Gold. This insulation, combined with stretchy and breathable inner and outer fabrics, makes the Nano Air unmatched for high energy activities. We understand FullRange is identical to the Toray branded 3DeFX+™ insulation, but we don't see 3DeFX+ used in any other products currently available in the North American market.
Polartec Alpha is another relatively new insulation on the market. Polartec Alpha, like FullRange, is a more breathable insulation capable of handling a larger temperature range. This insulation is unique, as the fibers are knitted into a sheet. The Outdoor Research Uberlayer uses Polartec Alpha.
When studying overall insulation structure, the most unique technology we reviewed is ThermoBall, developed jointly by The North Face and PrimaLoft. While the fibers used are similar to the other insulation, they are organized as small spheres rather than batts. These small fuzzy balls of fiber fit together much like goose down and need to be captured in pockets of fabric (baffles) in the same manner.
An Insulated Jacket to Meet Your Needs
Light, Medium, or Heavy Insulation
To determine how much insulation and warmth you need, first consider what kind of weather you usually play in and what your typical layering system usually looks like. Most folks, whether hiking, backpacking, skiing, or alpine climbing will pair one of the light or medium insulated jackets with a hardshell or rain jacket for cold weather. Imagine you're hiking when it's near freezing and drizzly out - you're likely wearing an insulating layer with a waterproof/breathable shell over top. If you're the type of person who hikes slowly and stops frequently to take photos, then a medium weight insulator like the Nano Air Hoody or the Nano Puff Hoody will serve you well as that mid-layer. A fast hiker who takes few breaks would probably overheat with more insulation, and instead should opt for a lightly insulated model like the Outdoor Research Cathode Hooded Jacket or the Arc'teryx Atom SL.
Long backpacking trips and big alpine missions place a premium on weight and space. Lightly insulated jackets, like the Rab Xenon X Hoodie, which delivers great warmth for the weight are appreciated. The Nano Air Hoody paired with the Outdoor Research Helium 2 rain shell would be a versatile, light-and-fast combo. If you primarily want an insulated jacket to keep you warm in camp or while belaying in below freezing conditions, the heavy weight Patagonia DAS is the warmest model we tested. Layer it right over the top of everything you're wearing.
Breathable or Wind Resistant
In our full review, we detail the continuum of light insulated jackets that range from super breathable to more wind resistant. When you want to wear your jacket as an outer layer, the type that will work best for you largely depends on what you expect out of it. Very breathable models like the Nano Air Hoody and Uberlayer work great for folks that push hard and generate a lot of sweat. No more taking your warm layer on and off to manage overheating. However, you'll need to break out a light Wind Breaker Jacket if the wind starts ripping though. Models in the middle of the continuum, like the North Face Thermoball Hoody and Nano Puff Hoody strike a balance. They won't handle high output activity as well, but do a better job blocking the wind. The Rab Xenon X and Patagonia DAS Parka, the most wind resistant jackets in our review, are also very water resistant. Their useful range as a terminal layer extends much further into windy and wet conditions.
Hood or No Hood
Do you want a hood on your jacket? When we asked our friends and fellow testers, we heard mostly "Yes." A hood adds significant warmth and weather protection for a small price in weight. Hoods are cozy warm around the neck too, and a hood is much harder to lose than a hat. This year, we only tested models with hoods, but most of the lightly insulated jackets are available without hoods as well. Some folks do not like the bulk of a hood under their shell jacket, and a hood flopping around on your shoulders while snow falls can fill right up with the cold stuff.
Stuffing & Clipping
Some folks will have a strong preference for an insulated jacket that stuffs away into its own pocket. This provides a quick and convenient way to compress a jacket and stuff it into your pack. Jackets that have a clip-in loop after stuffing are super nice for easy access when climbing. The Xenon X stuffs fairly small and has a secure clip-in loop; it's one of our favorite climbing jackets.
Layering & Sizing
It is common to wear a lightly insulated jacket as a stand-alone layer when it's chilly and clear and to add a waterproof/breathable shell over top if the weather turns nasty. An insulated jacket worn this way will be warmest when sized to fit fairly snug, eliminating air pockets between the layers. A lightly insulated jacket is more likely to end up as a mid-layer and should be sized accordingly so it will fit under a rain shell. The heavily insulated and waterproof models like the DAS Parka are intended to be worn as a terminal layer and should be sized to fit over everything you're wearing. As with any jacket, be sure to test the arm length, move around, and raise your arms overhead. Some of the products we tested have a tendency to ride up, while others will still keep your waist warm while you reach above.