What Is Down Fill Power in Jackets?


Today online when we shop Down Filled kit were bombarded with numbers from 150,650,800,100,1200 fill. And a load of construction types and styles from sewn through Baffle to Box baffle and the list goes on.

When considering a new down jacket, don’t get sidetracked by the colour instead focus on its construction. It is important to understand what makes them so effective at keeping you warm. Below i’ve written some of  the main factors that you should be considered when choosing the perfect down jacket.

What Does Down Fill Power Tell You?

Fill power is a number that indicates the relative quality of down. The number comes from a lab test that measures how many cubic inches of loft one ounce of that down fill produces. Higher fill power numbers indicate greater loft and insulating efficiency. (It’s important to note that down fill power does not tell you how warm a jacket or a sleeping bag will be because too many other factors affect warmth, including how much of that down fill is in the jacket or bag.)

Lofty Down is Warm Down

Down’s reputation as the ultimate insulating material for outdoor adventures derives from its ability to compress into a small, packable shape and then puff back up later. The key to down’s warmth is the formation of small air spaces within the down “plumules” (superfine featherlike plumage). Higher quality down fluffs back up to create more loft after compression, providing more heat-trapping air space within the down fill.

The Down Fill-Power Test abit tech but here we go. 

The test is typically done by filling a large cylinder with one ounce of down. A lightly weighted disk is placed on top, and begins to slowly sink and compress the down. After exactly one minute, the position of the disk is recorded and the volume of down compressed at that point is calculated.

A result of 450 cubic inches of down equates to 450-fill-power down. More resilient down compresses less and will loft higher. It also yields a higher test result—900 fill power is about as good as down gets.

Where High Fill Power Makes Sense

Premium fill-power down commands a premium price. It’s used to keep jackets ultralight and ultra packable. So if you’re trying to save weight and space in a pack or you want a super sleek winter jacket, a 900-fill-power jacket is worth considering. If overall weight and bulk aren’t important to you, get a super puffy jacket and don’t worry if it only has 500-fill-power down. 

Fill Weight: An Important Spec You Rarely Find – important if climbing super high. 

A 900-fill-power down jacket that has only 30g of down fill won’t be warmer than a 450-fill-power jacket with 100g of down fill. In theory, 50g of 900-fill-power down would be the same warmth as 100g of 450-fill-power down; it would also compress to about half the space. Very few jacket makers report fill weights, though. And any simple formula for warmth calculation won’t account for differences in how the down fill is distributed within baffles and around the jacket. 

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.

Down Fill Power and Synthetic Fills

Synthetic fills have no equivalent test to down fill power, and each brand of synthetic insulation has unique characteristics. So, it’s not possible to use down fill power to compare insulation efficiency to any synthetic fill, and there’s no way to compare the efficiency of two different synthetic fills.

Synthetic insulation

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.

The Rest of the Warmth Story

Your other clothing layers, the jacket’s shell material and many other design details also figure into how warm you will feel. Couple that with differing metabolisms of people and widely varying weather they might encounter, and you can understand why a temperature rating on a jacket wouldn’t be meaningful.

Final Thoughts

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 anything can be expensive. To choose that it 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 filled will allow you to make better decisions when purchasing your perfect item.

Hope this helps


How to choose the right Sleeping bag for you  Down vs. Synthetic: Which Insulation is Right for You?


By Jason Black

By Jason Black

Jason spends a great deal of his time sharing his experiences, inspiring communities to believe in themselves, strengthening self-worth and finding real purpose in life.

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