While synthetic fibres have been used as an alternative to natural fibres for clothing for decades, synthetic insulation has long failed to hold a candle to duck or goose down. Indeed, high quality down still reigns supreme in terms of warmth for weight but years of research and development with synthetic means the gap is no longer the gaping chasm it once was.
The drastic improvement of synthetic insulation has gone hand in hand with customer demand. The environmental impact of synthetic insulation and fibres has its own challenges, but more and more people are turning to it because of their discomfort with buying jackets and sleeping bags stuffed full of bird feathers.
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Here, we are looking at the very best synthetic insulated jackets for hiking in the UK. Each garment has its own strengths and weaknesses because they are all focused on offering something slightly different, be it maximum breathability, compactness, comfort, or weather protection. We've also included all the information you need to know to help make you more astute when buying your next synthetic insulated jacket.
What is synthetic insulation?
You will likely know what down feathers look like, the small, delicate and fluffy feathers that sit beneath a bird's outer feathers. They're extremely effective at trapped air pockets that create a warm air blanket for the bird. This is why they are looked upon with envy by humans.
Synthetic insulation is not fake feathers, though it tries to copy its traits as closely as it can. Synthetic insulation is usually made from polyester (hopefully recycled rather than raw). It's not quite as delicate and therefore light or compressible as down but the fibres are arranged to intertwine and trap air pockets just like down does.
Down vs synthetic
Down remains lighter and warmer than synthetic insulation. Where down uses fill power to determine its 'fluffiness', synthetic does not use this or an equivalent measurement, so it is tricky to say exactly when a certain synthetic insulation is the same as 600-fill down, for example.
Down is also more compressible than synthetic insulation, which comes in handy when stuffing your insulated jacket into your rucksack.
But anyone browsing shelves or online shops will have quickly noticed the price difference between down and synthetic insulation. The latter is considerably less expensive. One of the other big advantages of synthetic insulation is its ability to keep its insulating abilities when it gets damp. For down to repel moisture it needs hydrophobic treatment, which many outdoor brands add to the down insulation of their hiking jackets.
Key features to look for in synthetic insulated jackets
Insulation: There are two types or styles of synthetic insulated jackets: those for warmth, like puffer jackets, and those more for breathability. The former use down-style fill in baffles and the latter use panels of insulation instead. Curiously, puffer-style synthetic jackets are warmer and more packable thanks to the compressible nature of the insulation. The panel-type insulation allows thinner and more stretchy fabrics to be used but this style doesn't pack down as well.
Breathability: This is strongly related to insulation type. Synthetic insulation that mimics down is less breathable than the thinner panel insulation. It's also important to consider shell and lining material too. Pure nylon fabrics are not as breathable as those that use stretch and sweatshirt-type fabrics.
Weight and size: This matters when hiking. Space is scarce. Synthetic insulated jackets are heavier than down but they can still be reasonably light in return for a loss of warmth.
Fit: Down-style synthetic jackets are great for layering underneath because they tend to have a looser fit. Meanwhile, those that use stretch fabrics have a more athletic fit, intended to use as a mid layer in winter or outer layer in milder temperatures. Personal comfort preferences are important here too.
Hood: A hood protects your head against heat loss. In winter, the hood of an insulated jacket is usually worn over a beanie, or over a climbing helmet when mountaineering. Most hoods are elastic-bound for a closer fit, but more technical jackets may feature two- or three-point drawcord adjustment.
The best synthetic insulated jackets reviewed
Rab Generator Alpine Jacket
Verdict: Protective but impressively packable belay-style parka that is perfectly equipped for UK winters.
Features 5/5 | Fit 5/5 | Comfort 4/5 | Performance 5/5 | Value 4/5
Overall score: 92%
Pros: Warm, packable, hard-wearing, moisture-resistant synthetic fill
Cons: Pricey for a synthetic jacket, no women’s version
Winner not only of the synthetic insulated test but also our overall insulated winter jacket test. This jacket features the latest innovation in synthetic fill, PrimaLoft Gold with Crosscore. Its polyester fibres are infused with aerogel, an ultralight material developed by NASA to insulate space shuttles. The resulting fill is up to 52% warmer than standard PrimaLoft Gold, with performance comparable to 750+ fill power down in terms of warmth for weight and compressibility.
It gives excellent all-round protection and coverage thanks to a roomy hood, drop tail and cinchable cuffs that work well with gloves/mitts. Other features include a zipped outer chest pocket and two zipped handwarmer pockets. Alas, they’re not fleece-lined but are placed high enough to stay out of the way. Inside, two dump pockets are perfect for temporarily stashing gloves or a flask.
This ticks plenty of boxes as a warm winter layer for stop-start mountain days. It also feels pretty tough, thanks to a Pertex Quantum Pro shell. The front of the jacket uses Diamond Fuse fabric, with interlocking yarns for better abrasion resistance compared to standard ripstop nylon. A DWR finish adds water resistance too. For a synthetic jacket, it is also remarkably compressible, comparable in pack size to Jöttnar’s Thorne down jacket.
Insulation PrimaLoft Gold Synthetic Insulation with Cross Core (133gsm body / 80gsm hood) containing 74% post-consumer recycled material | Shell 20D Pertex Quantum Pro nylon 40gsm (Diamond Fuse front/Recycled back) | Sizes men’s XS-XXL, women’s n/a | Weight 540g (men’s M)
Verdict: For many this would be ideal to throw into the rucksack in winter when heading to the hills, but there are some drawbacks.
Features 3/5 | Fit 3/5 | Comfort 4/5 | Performance 4/5 | Value 5/5
Overall score: 80%
This is a great warm jacket for throwing on at the summit. It’s packed with Primaloft Thermoplume insulation, which is said to offer similar performance to 500 fill power down. The nylon Pertex Eco outer fabric fends off the wind well too. The sleeve movement is superb, without a hint of the cuffs or hem riding up. The two main pockets are well-placed so you can access them easily even if wearing a rucksack, and there is a third chest pocket for a GPS receiver. A nice touch is a section of soft brushed material at the top of the zip to protect against any rubbing of the chin. In many ways this performs almost as well as those with more chilling price tags.
It is a little heavier than others (and note this was a size medium, while others are size large), but also others have additional features. So for example the hem and the cuffs do not get any adjustment apart from elastication. The hood has no adjustment either, and while it did fit well it did not move at all with the head. A more subtle aspect of the jacket is that the fabric feels a little stiffer than some others with higher price tags, so it feels just a little less comfortable to wear. The price is not the lowest either.
Insulation Primaloft Thermoplume | Shell Pertex Quantum Eco 50% recycled | Sizes men’s S-XXL (Icarus), women’s 8-16 (Phoenix) | Weight 605g (size M)
Patagonia Nano Puff
Verdict: It ain't cheap but it is an exceptional jacket in terms of performance and sustainability.
Features 5/5 | Fit 4/5 | Comfort 4/5 | Performance 4/5 | Value 3/5
Overall score: 80%
Pros: Excellent all-rounder, warm, durable, eco
Cons: Pricey, some may want a slimmer fit
The Nano Puff has enjoyed the luxury (achieved through being very good) of remarkable widespread popularity. It's been updated over the decade or so it's been around, primarily focusing on improvements within its supply chain and product design developments to reduce the environmental impact of one of its most adored products.
Everything about the Nano Puff serves a function. The brick quilting pattern isn’t just for show. The narrow horizontal quilt lines on side panels stabilise the insulation and uses durable thread for abrasion resistance. The main zip has a wicking interior storm-flap and zipper garage at the chin for next-to-skin comfort. The two handwarmer pockets have zip-closures with zipper garages. The zipped internal chest pocket doubles as a stuff sack with a reinforced carabiner clip-in loop.
The Nano Puff doesn't offer the weather protection of Rab's test winner or Black Diamond's Belay Parker (below) but as a synthetic insulated jacket, it's about as close as offering all things to all people as one could reasonably demand.
Insulation 60g PrimaLoft Gold Insulation Eco, 100% post-consumer recycled polyester with P.U.R.E. (Produced Using Reduced Emissions) technology | Shell 20D 100% recycled polyester ripstop with a DWR (durable water repellent) finish | Sizes men’s XS-XXL, women’s XS-XL | Weight 337g (size M)
Black Diamond Belay Parka
Verdict: A beast of a jacket, providing fortress-like protection and warmth, but the trade-off is that it is a bit of a lump.
Features 5/5 | Fit 4/5 | Comfort 5/5 | Performance 4/5 | Value 4/5
Overall score: 88%
Pros: Extremely warm, moisture-resistant synthetic fill, great hood
Cons: Bulky packed size, hefty weight
This classic belay jacket takes a simple approach to warmth: pack a ripstop shell chock-full of sheet insulation. Thick 200gsm Thermolite fill makes this one of the cosiest synthetic jackets around. It’s pretty much like wearing a sleeping bag, so you shouldn’t be cold even in sub-zero temps.
As an over layering piece, the fit is generous, so you might want to size down. Note that the same fill weight is packed into the body, arms and hood too – there’s no body-mapping here, which doesn’t make for a svelte silhouette, nor, if we’re honest, optimum mobility. Then again, it’s designed for static use, and in that capacity it excels whether you’re hunkered down in a summit shelter or belaying a climbing partner in a windswept gully.
It’s worth highlighting the hood too, which can make or break an insulated jacket. This one is brilliant. It works with or without a climbing helmet and is exceptionally warm. Adjustment is via a single rear drawcord, but this simultaneously reduces the hood volume and pulls it in around the face too. We also liked the fleecy hand pockets, the useful two-way main zipper and the large inner dump pockets.
Downsides? Inevitably, weight and bulk. This one’s going to fill the bottom of a rucksack, even if you’re toting a big winter pack.
Insulation Thermolite HL Eco-Made Synthetic Insulation (200gsm) | Shell 50D ripstop polyester 80gsm with PFC-free DWR | Sizes men’s S-XL, women’s XS-XL | Weight 845g (men’s M) / 718g (women’s M)
Patagonia Nano-Air Hoody
Verdict: Very comfortable and breathable - ideal for high-output hiking sessions. But it's rather expensive.
Features 4/5 | Fit 5/5 | Comfort 5/5 | Performance 4/5 | Value 3/5
Overall score: 84%
Pros: Very comfortable, very breathable, surprisingly warm
Cons: Expensive, not the most durable
If it's comfort and breathability you seek, your answer is found in the form of the soft, stretchy Patagonia Nano-Air Hoody. Predictably, it's a relatively slim fit, using Patagonia's FullRange insulation rather than fake plumage. It's certainly light when you wear it and supremely comfortable but it doesn't pack down like the Nano Puff, for example.
There are plenty of features we like. The chest pocket is a nice touch; the comfy, removable hood helps add that bit of extra warmth without adding much bulk; and it does still have a stuff sack to keep it compact. Climbers will certainly appreciate the pockets positioned high enough to still use while wearing a harness.
In line with Patagonia's ethos, the Nano-Air uses mostly (87%) recycled polyester for the shell and the insulation is 40% recycled. Like the Nano Puff, it's not a cheap garment but then, you are getting a lot in return.
Insulation 60g FullRange polyester (40% recycled) | Shell 33D polyester (87% recycled) with PFC-free DWR | Sizes men’s XS-XXL, women’s XS-XL | Weight 346g (men’s M)
Verdict: A solid addition to your hillwalking kit – weatherproof and well-priced. Not as light or warm as some rivals though.
Features 5/5 | Fit 4/5 | Comfort 4/5 | Performance 3/5 | Value 5/5
Overall score: 84%
Pros: Durable, versatile, weatherproof,
Cons: Not the lightest, not as warm as others
You can’t always trust a brand’s own product descriptions when it comes to outdoor kit. But Alpkit says the 0Hiro provides ‘safe refuge from cold and damp British winters’. And to be fair, that pretty much nails it.
This is stands alongside the Black Diamond jacket above as the most weatherproof and hard-wearing of all the jackets here, thanks to a tough ripstop nylon shell backed with a waterproof membrane. This protects the PrimaLoft Silver Hi-Loft Ultra synthetic fill from becoming waterlogged, though the insulation itself is fast-drying and moisture-resistant. Admittedly, it isn’t quite as thermally efficient as some. But with fill weights of 120gsm in the body and 80gsm in the arms and hood, it’s still a viable winter layer, and one that will outperform plenty of pricier rivals on a cold and wet mountainside – we’d certainly pack it ahead of a down jacket if the forecast threatened rain. So, the 0Hiro has much to recommend it.
We tested the women’s version, which fits true to size, but size up if you want to use it as a belay-style overlayer. It has plenty of pockets, including two roomy inner dump pockets for gloves or mitts. The adjustable hem and stretchy cuffs are great, as is the soft chinguard, handy two-way main zip and helmet-compatible hood (which has three-way adjustment and a wired peak).
Insulation PrimaLoft Silver Hi-Loft Ultra (120gsm body / 80gsm arms and hood) | Shell 100% 6.6 nylon with a 5K/5K TPU waterproof-breathable membrane | Sizes Men’s S-XXL Women’s 8-18 | Weight 690g (men’s M) / 630g (women’s 12)
The North Face Eco ThermoBall
Verdict: A solid rival to the Patagonia Nano Puff, just not quite as light.
Features 4/5 | Fit 4/5 | Comfort 4/5 | Performance 4/5 | Value 3/5
Overall score: 76%
Pros: Many colours, good eco credentials, versatile
Cons: Quite slim not ideal for layering underneath, quite pricey
The North Face's cute-sounding Eco ThermoBall is a solid competitor to Patagonia's Nano Puff. They are priced the same, have the puffer style, are versatile, and have good eco credentials.
Like the Nano Puff, the ThermoBall also uses recycled insulation developed with PrimaLoft, so it's similarly warm, but the ThermoBall does weigh a little more. We like the zipped pockets (stuffs into the chest pocket) and cuffs - there's no reason why you couldn't use this every day as well as in the hills.
It's fabric doen't feel quite as durable as the Nano Puff's and that along with its extra 80 grams or so of weight does mean the ThermoBall is bested. However, it's still an excellent and versatile synthetic insulated jacket for many uses.
Insulation ThermoBall Eco 100% recycled | Shell 20D 100% recycled nylon | Sizes men’s S-XXXL, women’s XS-XXXL | Weight 450g
Synthetic jacket care
It is true that synthetic insulation is easier to care for that down. You can pop it in the washing machine with normal detergent rather than using a special down wash. But you must also realise that synthetic insulation is not as durable as down. Cared for down products last decades. Jacket and sleeping bags with synthetic insulation will not maintain their insulating abilities for this long.
Many people switch from down to synthetic out of animal welfare concerns and cost reasons. While turning to synthetic does indeed negate the need for down, there are other challenges that loom large in its place.
Chief among these is the plastic problem. The world already has too much plastic and filling your jacket with it seems to exacerbate the problem. It's therefore important to buy synthetic jackets with recycled insulation so that at least more plastic isn't being created by your demand.
It hasn't taken long for the industry (or at least the part of it that cares) to come up with biodegradable fibre. PrimaLoft Bio is a world-first fully biodegradable fibre that breaks down in landfills, oceans and wastewater and is now being used as insulation and a clothing fibre.