Understanding Fill Power

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When you’re shopping for a down comforter, you see many terms and numbers thrown around. One of the most confusing is “fill power.”

What are the numbers associated with fill power when it comes to bedding, and what do they mean when it comes to your comfort? We’ve got all the answers in this brief guide to fill power.

What Is Fill Power And How Is It Measured?

Down creates warmth by trapping heat in its air pockets. The loftier the down, the more heat the down can hold.

understanding fill power closeupGermanova Antonina/Shutterstock

Fill power is a measure of loft. Specifically, it refers to the amount of space one ounce of down fills at its maximum expansion.

To determine the fill power for a particular down, one ounce of that filling is placed within a calibrated chamber. If the down takes up 650 cubic inches at its full loft, the fill power will be 650.

What Is Good Fill Power?

One ounce of higher-fill-power down is going to have more space to trap heat than one ounce of lower-fill-power down. So, as a general rule, higher-fill-power down will give you more warmth. If that still feels confusing, consider the following metrics:

  • The 400 to 450 range is going to be medium quality fill power, while 500 to 550 is considered good
  • 550 to 750 is considered very good, while any fill power of 750 or above is considered excellent

How Does This Interact With Fill Weight?

Here’s where things get confusing: Just because you have a comforter with high fill power, that doesn’t mean it is going to be warmer than a comforter with low fill power.

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understanding fill power comforter close upFreebird7977/Shutterstock

That’s because the weight of the fill must also be taken into account. So a comforter with 30 ounces of 700 fill power down may not be as warm as a comforter with 60 ounces of 550 fill power down.

What Does Fill Power Mean For Down Alternative Comforters?

Even though most down-alternative comforters advertise their fill power, their synthetic fill cannot really be measured by the same criteria as natural down.

In addition, each synthetic fill is different, so it is difficult (if not impossible) to compare the fill power of two distinct kinds of synthetic fills.

Overall

More likely than not, you will pay more for down with a high fill power. However, just because a comforter has high fill power, that doesn’t necessarily mean it is the right down comforter for you. Consider the fill power, fill weight, and what kind of sleeper you are when deciding on a new comforter.

Featured image: lightmood/Shutterstock

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Marten Carlson

Marten Carlson

Lead Mattress Reviewer

About Author

Marten has been writing about mattresses and sleep health for six years. He is the lead reviewer at Mattress Clarity where he tests mattresses, bedding, and sleep accessories.

In his role here, Marten’s reviewed over 500 mattresses and 150 sleep accessories (so you can rest assured that if he recommends a product, it’s been put through the wringer in our Austin studio). In addition, he has written more than 400 articles reviewing the quality of sleep and sleep products as well as sleep health. He’s especially interested in the correlation between sleep and mental health.

Marten’s also got a personal stake in sleep health. After writing dozens of pieces on the dangers of sleep apnea, he decided to get tested for the condition. Realizing he did, in fact, suffer from sleep apnea, he immediately started using a CPAP machine. He knows all too well the importance of a healthy night’s sleep and is passionate about helping others get the healthy, restorative sleep they deserve.

He received his bachelor’s degree in Film Production from Denison University and his master’s degree in Film Studies from Emory University.

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