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Not all down is created equal, and higher quality down can lead to more comfort and better sleep. It would be nice if the nebulous concept of “quality” could be reduced down to a single number. It can’t, but there are a couple of metrics you can use to better gauge your pillow’s quality.
The first is fill power. This measures how much air is trapped in a single ounce of down feathers. If one ounce of (uncompressed) down takes up 500 cubic inches, then it has a fill power of 500. This factor contributes to how fluffy the down is, as well as how much heat it traps. This can be a tricky number to rely on, because some products like down-filled jackets are designed to keep heat in, so more fill power is better.
With pillows, on the other hand, while more fill power means more fluffiness, it can also mean more heat gets trapped, leading to a never-ending search for the cool side of the pillow. In some cases, you’ll find that pillow manufacturers have stopped including the fill number in their descriptions, specifically to avoid this confusion.
That’s where fill weight comes in. This can often be confused with fill power, but instead it refers to how much down is in the pillow, measured in ounces. So, for example, a pillow with a lower fill weight might have 12 ounces of down, while a higher fill weight pillow might have 20 ounces. Both fill power and fill weight can contribute to how fluffy or firm a pillow is.
Most pillow manufacturers will eschew displaying either of these numbers too prominently, and instead offer selections for two or three levels of support. While we take these factors into consideration while testing, your best bet when buying any pillow is to consider how you sleep—on your side, your back, etc.—and pick the fill level that’s most likely to keep your head and body supported in a way that suits you best.
