Down consists of clusters of filaments growing and radiating from a central quill point, but without a quill shaft. Its three-dimensional structure allows it to make thousands of air pockets, called loft. This will trap air, making down the perfect insulator for winter jackets. Another advantage of down is that it is highly resilient, able to resist damage caused by compression. In particle terms, this means it can be stuffed into a bag again and again, and it will never lose its ability to keep the wearer warm.
When considering a new down jacket, it is important to understand what makes them so effective at keeping you warm. Below are the main factors that should be considered when choosing the perfect down jacket.
The measurement of a down product’s loft in relation to its insulating value is known as its filling power. A higher filling power means more air can be trapped in a specific weight of down, thus creating greater insulating properties. Filling power rating is usually measured by calculating how many cubic inches an ounce of down will cover. For example, a down rating of 500 means one ounce of down will cover 500 cubic inches.
Most common down products have a rating between 400 and 500, but the range can vary between 300 and 900+. When looking for a high quality down-fill jacket, it is normal to look for a filling power in excess of 550, and for superior warmth and performance a jacket needs to have a filling power of 900 or higher.
Weight will be an important factor in most clothes purchasing decisions. A jacket must match the requirements of the buyer. For example, for backpacking and outdoor travel, a lighter jacket will often be preferred. This is where filling power becomes important as, to provide the same warmth, a down jacket with 500 filling power needs to be bulkier and heavier than a jacket of 800 filling power. Higher filling powers can therefore equate to lighter garments but there does need to be a trade-off between filling power and weight, which can depend upon the jacket’s function.
Percentage of down
The percentage of down in a jacket will affect the insulating ability of the jacket. Normally represented as 80/20, 90/10, etc. this symbolizes the split between down, known as the down cluster, and feathers. For example, 80/20 would mean 80% down and 20% feather. High quality products will normally have a higher down percentage, but this will be reflected in the price as down is more expensive. Because down is a better insulator, two jackets with 750 filling power will not necessarily keep the wearer as equally warm – if one has 90/10 and the other 80/20, the first will be warmer.
Construction – down baffling method
There are two main quilting methods for down jackets:
- Sewn-through baffle
- Box baffle
The most common method is sewn-through baffle, which involves stitching around each baffle’s edge that goes right through the garment – from outer to inner layer. This method is easier to make and it keeps the down securely in place. It is therefore the most commonly used method but it does have one major drawback – the outer and inner layers will be drawn together by the stitching, reducing the loft amount and causing loss of warmth.
Box baffle is more difficult to construct as it allows each baffle to have its own three-dimensional rectangle. This reduces pinching at seams and therefore allows maximum possible loft, giving better insulation.
DWR treatment of down
The principle downside of down is that it tends to stick together and lose loft when made wet. When this happens, it will lose its insulation properties. The traditional response to this has been to seal it within a fabric membrane but this means losing the advantage of down’s natural breathability.
More recently, treatments have been introduced that will allow the down to resist light moisture. These are durable water repellents (DWR) that work at a microscopic level. They will, however, not resist submersion or a heavy downpour.
Simulated down is becoming a common alternative. It has the benefit of maintaining its properties when wet, will dry quickly, and it generally more moderately priced. There are currently many innovations in synthetic insulation, including a newly developed microfiber material that closely mimics the look and feel of natural down but, when wet, has double the loft of natural down. It is also lightweight and highly breathable. With advances like these, the gap between synthetic and natural is diminishing.
Shell and lining material
When choosing an insulated jacket, it is important not to forget the shell and lining materials. These can have a profound effect on durability, weight, warmth, and water resistance. For an outdoor jacket, it is important to choose a breathable shell fabric that will allow perspiration. If this is neglected, moisture will be trapped inside the jacket, dampening the down.
Nylon and polyester are commonly used for outer layers, since they are durable and can withstand harsh conditions. It is important, however, to inspect a jacket before purchasing to ensure no feathers are leaking through the shell fabric, lining, seams and/or stitching. A good tip, when buying a down jacket, is to choose one with an extra layer laminated onto the fabric. This will increase the jacket's ability to prevent down and feather leakage.
Finally, choosing a jacket can also be a matter of choosing which additional features you need. Many down jackets will have hoods, zippers, pockets, adjustable hems, etc. It is important to consider whether they are necessary for the function. If the jacket has zippers, they should ideally have overlapping panels to reduce heat loss.
When looking at pockets, it is again important to consider function. Do they need fasteners to secure articles? Are they suitable for keeping your hands in, in the cold? Keeping warm is the main function of a down jacket, so any additional features, for example adjustable hems, hood and cuffs, will help to keep you warm in winter.
Buying a down jacket can be expensive. To choose a jacket that fits your requirements, it is important to consider all aspects of its design and manufacture, including material, filling power, down percentage and weight. Learning about the different types and designs of down jackets will allow you to make better decisions when purchasing your perfect down jacket.
For more information:
Senior Technical Service Manager
Consumer and Retail - Softlines
SGS Hong Kong Limited
t: +852 2765 3695