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admin23/03/2010 15:48:58

Compston CornerAmbleside Cumbria LA22 9DS

Down vs Synthetic

   Words by tcsh

   on 26/08/2010 12:57:00

If you are looking to get yourself a good piece of insulation, be it a jacket or sleeping bag, this is a question you will need to ask yourself. Traditionally, the answer was easy, if you wanted to actually stay warm then down was the way to go, however recently, synthetic insulation has caught up somewhat, making the decision not so straightforward.

Here, we will try and lay out the fact for you in as simple terms as possible so that you can make the decision as easily as possible.

How Does Insulation Work?

Haglofs-Barrier-WS-MangoAll insulation works in the same manner, by trapping a layer of warm air next to your body. Even when it is very cold, we produce warmth from our body. The reason why you might feel cold is that, in very cold temperatures, that warmth is instantly cooled by the environment and you then have to use up more energy producing more warmth.
If you put a layer of warm air around you then your body does not have to keep producing heat to keep you alive, it can now produce heat to actually warm you up. How good an item of insulation is depends on how well it can trap that layer of warm air. Does the wind get in an blow some of it away? How deep in the layer of warm air? How quickly does it warm up?

What are Down and Synthetic Insulation Actually Made Of?

Down Insulation:

In danger of stating the obvious, down insulation is made of … down!

More specifically, the downy feathers from either ducks or geese. Down is actually the soft and fluffy fibres that lie under the feathers of a bird. These have one job, and that is to keep a bird warm, which is obviously why they are so useful to us. The filaments in the down fluff up and are very efficient at trapping the air next to the body and allowing that air to insulate you – this is know and lofting.

(Top Tip: If you have a Down jacket that keeps losing feathers as they poke through the outer fabric then that is a sure way to know that it has got cheap down in it. Real down has no spine to it)

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True Down vs a ‘Downy’ Feather

Synthetic Insulation:

Synthetic insulation is an attempt to artificially emulate the natural properties of down insulation. Long fibres of polyester are woven into a mat which then contains millions or miniature gaps which trap the air efficiently and consistently. In some cases, these fibres are also hollow which traps even more insulating air.

Is There Just One Type of Down and Synthetic Insulation?

You know it wouldn’t be that simple! No, there are loads of variations, but we’ll try and keep it simple here.

Down Insulation Types:

The two main types of down insulation are Goose and Duck. It is generally accepted that goose down is the higher quality, as it lofts better.

When looking at down items you are often confronted with various numbers, including fill power and down grade. These are good indications of the quality, as long as you understand them.

Down Fill Power

Down fill power is recorded with a single number (600, 650, 750 etc) and is a measure of the loftiness of the down. The number refers to the number of cubic inches that 30g of down occupies when under an international standard of pressure. A higher number means that the down lofts more and occupies more space which will in turn make it more insulating when it’s used in a jacket or sleeping bag. Medium quality down tends to have a number of around 550 whereas the better quality items have a number closer to 700 or 750+.

(Top Tip: The US Fill power is not measured in the same manner as the UK and therefore their numbers tend to be higher for the same quality of down. Be careful if comparing a UK brand jacket to a US one as the numbers will not correspond (US will be higher by about 100))

Down Grade

The quality of the down is not just related to the species of bird, it is also a reflection of the ratio of down to feather that the manufacturer uses. Lower quality down is sometimes bulked out by using downy feathers which give a bit of extra loft but without the warmth. The top quality down products have a ratio of around 95% down which is normally expressed as 95/5, where the first number is the down and the second is the feather. Pure 100% down is virtually unachievable as it would be so labour intensive that it would make the down incredibly expensive.

Down Facts: Quality can also depend on age – a mature duck will produce better quality down than a young goose – however there is almost no way of knowing the age of you the down so we just stick to Goose=Better.

The down is a bi-product of the poultry industry and therefore the price of down jackets and sleeping bags is directly connected to how popular duck and goose meat is in Europe and the Far East.

Synthetic Insulation Types:

If you thought down could get complicated then synthetic insulation can present you with a bewildering array of options. Essentially, all synthetic insulation works on the same principle but as with most technology, the specific details are always well guarded secrets. Fortunately, the top brands have done the investigating and testing for us and come up the with market leaders.



In the UK, this is the the leading brand of synthetic insulation. It is very thermally efficient, highly compressible and has excellent water resistance. Without buying down, this is probably as close as you will get. The actual make-up of branded synthetic insulation is a often a closely guarded secret so it is hard to tell you too much about the composition.



A major brand in the US market, many companies in the UK also use they insulation, although they do appear more in the gloves and accessories ranges.

Many brands produce their own insulation types which will be based on the same principle as Primaloft but just cost the company less to purchase.

Well what are the pro’s and con’s of Down and Synthetic Insulation then?

Down Insulation

Synthetic Insulation


Very warm


Extremely compressible


Warm, even when wet

Dry’s quicker


Holds its shape



Loses warmth when wet

Slow to dry and can ‘clump’

Can move around and needs baffles to keep it in place


Heavier than down

Not as compressible


This basically means that the two types of insulation can fulfil slightly different niches;

A down jacket is more suited for very cold, but dry environments – this is why you find down jackets are the choice product for high altitude, alpine or polar expeditions. In these situations, the down’s better thermal capacity comes into it’s own and there is little chance of the down getting wet as any water is always frozen as ice or snow. In order to insulate against the extreme cold of these conditions, a synthetic item would have to be so big that it would not be practical to wear.
A synthetic jacket however is much better suited for a slightly more mild climate where temperatures can still get well below zero but, at lower altitudes, or at certain times of day, you can also expect rain or wet snow. In these conditions the insulation that a synthetic item provides is perfectly good, and the water resistant fibres make it a better choice in the damper climate. Synthetics are therefore a far better choice for UK winter use.

Is there a difference in how you look after Down vs Synthetic jackets?

As you can imagine, washing a down item is a little harder than washing a synthetic garment – although the down composition is better these days, you still need to be careful that you don’t clump up the down and leave yourself with cold spots where there is no down. For the full run down of how to wash them, then take a look at our Washing & Reproofing Guide.

Hopefully that has cleared up some of the confusion that can surround insulation. If you want more info on sleeping bag insulation in particular then take a look at our ‘Sleeping Bags Gear Guide’, and for more answers to questions not posed here then feel free to give us a ring on 015394 30122 or email us.

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