July 8


What is Fill Power?

What is Fill Power?

Since as far back as the 1600’s, down has been used by humans to insulate and protect themselves from the cold. Down, once used only by those that lived in colder climates, is now a part of many products used by people around the globe, every day. The widespread application of down had created a need for an accurate way to rate the down being used and the “fill power” rating was developed to provide that information.

What does down fill power mean? How does it apply to the average consumer? Down fill power ratings are marketed on many products but what does it actually indicate and how is that relevant? Understanding the answers to these questions helps businesses and consumers make better decisions when buying down products.

Why is the Fill Power Important?

Down fill power provides a scale upon which you can evaluate the quality of the down in any given product. The better the quality of the down, the less down by weight will be needed to create the thermal retention desired. For applications of down where weight is important, such as jackets and sleeping bags, down fill power is particularly critical.

How is Down Fill Power Determined?

Down fill is an amazing insulator because of the air that is trapped between the fibers of the down and feathers. That means that how well the down keeps its volume under pressure is important. To accurately measure down fill power in the US, one ounce of down is placed inside a cylinder, upon which a weight is set, compressing it. The amount of volume left below indicates the fill power. 

Down of higher quality will be able to insulate better than the same weight of a down with lower fill power, making a higher fill power down more valuable per ounce. High-quality down is also able to be compressed and still bounce back and regain its “loft” (the volume it occupies in a given space). 

It is important to note that for all of its amazing qualities, down is particularly susceptible to moisture. If down gets wet, it loses close to all of its insulating properties and becomes almost useless. That is why the condition of the down when tested is crucial.

Conditioning Down for Fill Power Results

For down fill power results to be accurate, the down must be “conditioned”. Why would you need to condition down fill? Because down fill interacts with the world and the user and is affected through the moisture, temperature, compression and air circulation. Conditioning the fill imitates these conditions and gives you the most accurate fill power results.

Though many methods can be used to measure fill power, the majority of methods will first apply moisture, followed by heat similar to a wash and dry cycle. A test is then performed to rate the material’s down fill power. This is the fill power rating that will be used for marketing claims surrounding the product. Over time, fill power can drop but proper, regular care of those down products can return the fill power to close to its original rating.

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