When it’s freezing cold outside nothing beats a down jacket for its insulating properties. But what exactly is a down jacket and what makes it so warm? Find out answers to the most common questions and how to choose a down jacket that’s right for you in our down jacket guide.

What is a down jacket?

A down jacket is a jacket which has been insulated with the soft and warm under feathers from duck or geese. Down is a fantastic insulator as the loft (or fluffiness) of down creates thousands of tiny air pockets which trap warm air and retain heat, thus keeping the wearer very warm.

The down fill of a jacket will be either goose down, duck down or a combination of the two. Goose down is often regarded as the warmest and lightest but duck down jackets, or jackets with a combination, are often cheaper.

From base layers to jackets there are many categories, sizes and shapes of thermal insulation. Down is by far considered to be the warmest, lightest and most effective insulator available on the market. But what is it exactly?

Types of down insulation?

Down refers to the soft layer of under-loft found beneath the harder, exterior feathers of geese, ducks and other water fowl. This lofty plumage has a loose structure that helps to trap air against birds body’s to prevent heat loss and increase buoyancy. When used in insulating items such as jackets, gilets and sleeping bags  the structure of down, that previously allowed for thousands of tiny air particles to be trapped for buoyancy, is used instead for the formation of a highly breathable layer that allows for a high level of thermoregulation which helps to maintain the body’s core temperature.

Down is considered industry wide as the greatest insulator, over taking both synthetic and woolen fibers, due to its astonishing compressibility and incredible warmth to weight ratio. This means that, although the thermal garment in question may be light and thin this does not alter the results of its effectiveness as an insulating layer. Furthermore, there are varying degrees of down;

• High loft goose down – Originating from mature/ adult geese this is the finest quality of down due to the tendrils being large and softer than most other down. As a result of this, not only is the down loftier, it is also very fine in construction, making it the warmest but also the most expensive material.

• Goose down –A slightly less lofty material, this makes it less warm and thus less expensive.

• Duck down – Less fine than goose down. Duck down sits at the everyday, affordable end of the down scale making it the least expensive.

Although natural down is exceptionally resistant to harsh environmental factors such as wind and sunlight, it does have one downside. The plumage used within these garments has an incapability to repel water and moisture. In actual fact, down looses a large amount of its thermal insulation when wet. This is because the plumage clumps together and is often slow to dry. Commonly, the fill remains bunched and the clothing losses a large majority of its heat retaining capability due to it leaving un-insulated areas in the garment.

How does it work?

All materials, including thermal base layers, hard shell water proofs and sleeping bags are measured using the industry standard of either the clo or tog units.
The ‘clo’ unit is measure as 0.155 K M2/W (Kelvin per Metre squared over Watts), or the more common unit the ‘tog’ are measured as 0.645 clo.

The effectiveness of down clothing can be measured by referring to its ‘fill power’. Fill power is a measure of the loft or “fluffiness” of a down product that is loosely related to the insulating value of the down. The higher the fill power the more air an ounce of the down can trap, and thus the more insulating ability an ounce of the down will have. Fill power ranges from about 300 (in³/oz for feathers to around 900 (in³/oz) for the highest quality down, with the latter being both the warmest and lightest. It should be noted that the most commonly found fill is between 400 and  500, although this is often low quality down, useful for cold city days or to be used as casual winter mid layer it is highly insulating none the less. As we Move through the spectrum of fill, layers with the fill of 700 are made from higher quality loft, increasing in both functionality and price. Down counts of 900 or more are rarely found within shops as they are often reserved for the top end winter mountaineers, or those partaking in winter sports on a regular basis.

When examining a down item you will also be confronted by a percentage representing the fill, for example, 80/20 or 90/10.This information is important as it represents the balance between the down and feather. Due to the nature of the material it is nearly impossible to separate all of the softer down from the harder contour feathers found on the surface of the water fowl. With this information, you can clearly tell that the garments with higher percentages are warmer, lighter, will compress more and as the tag will tell you, they are often more expensive.

Down vs Synthetic

Down feathers are much lighter than synthetic insulation so down jackets tend to be very lightweight in comparison to a synthetic version. The sheer quantity of feathers used in a down jacket however will make a down jacket seem bulkier (they can be rolled or folded up into a smaller size by squeezing out the air).

If you are doing an active pursuit, such as hiking or skiing, a down jacket may cause you to heat up too much. If you are a naturally warm person a synthetic filled jacket may be a better option.

A down filled jacket is ideal for cold and dry days, but may not be suitable for wear in heavy rain. Many down jackets will have a water resistant outer layer but may not be 100% waterproof (our Antarctic down jacket is an example of a fully waterproof down jacket). Down does not perform well when wet as the feathers stick together and lose their loft, thus their ability to retain heat.

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Down is warm enough that ducks and geese can swim in freezing water and light enough that they can fly. It’s the best form of insulation yet devised for outdoor apparel. Down’s warmth, light weight and compactable form make it the perfect material for activities like skiing, mountaineering and backpacking. Advances in treating down also mean that down jackets are more resistant to down’s mortal enemy, moisture, than ever before. From lifestyle wear to burly mountaineering layers, down jackets are lighter, tougher and more water resistant than ever. These down jackets are perfect for every activity, from walking your dog in January to dodging polar bears at the South Pole.