What is Down Fill Power? How Much Fill Power Do I Need?


Whether you’re backpacking through the backcountry or skiing down a mountainside, it’s always important to protect yourself from the cold. When it comes to warmth there’s nothing quite like down filling.

A jacket or sleeping bag filled with high quality down will keep you warm in even the coldest temperatures. This is great, but with so many brands and styles, how can you tell if you’re buying quality gear? Luckily, there’s a little thing called Fill Power that measures the quality of your down jacket.

What is Down Fill Power?

Have you ever pondered between two similarly priced down sleeping bags(or jackets) unable to make a decision? How can you decide between down gear?

While diving into the technical specs of camping and backpacking gear you might see the term Fill Power thrown around. Fill power is a number that tells you the relative quality of down(higher is better). Simplifying things a bit, fill power measures the loft of a down product, which in turn tells you the quality level of the down.

How is Down Fill Power Tested?

Scientists calculate the fill power by measuring how many cubic inches one ounce of down covers at its maximum loft. Maximum loft only occurs when the clusters of down are fully expanded. The air between the plumage is what makes down insulation so effective.

For example, A fill rating of 700 means that 1oz of down can cover 700 cubic inches in a controlled setting. They basically just fill up a large cylinder with 1oz of goose down and slightly compress it with a weighted disk. The weighted disk slowly starts to compress and they record the volume.

High quality down is more resilient to weight than immature down. So quality down(high fill power) will compress less and loft higher. 900 Fill Power down is about as good as you’re gonna get, but it’s rarely used in consumer-grade gear.

Fill Power Range(Higher is Better)

Most of the down products on the market have a fill power between 300 and 900 cubic inches. A typical down pillow is usually between 400-500 Fill Power. This is actually considered to be very low quality down (coming from young immature geese).

When looking at camping gear aim for a minimum Fill Power of 550. Jackets and sleeping bags with higher fill power will be lighter, warmer and more comfortable.

Why is High Fill Power Down Better?

During the manufacturing process down is formed into clusters of filling to be used as insulation. These down clusters are made out of thousands of tiny down fibers that interlock trapping pockets of air between them.

This is what creates the loft effect which makes your gear warm. These down clusters trap air in a way that

Fill Power Affects Price(Sleeping Bags)

The overall price will depend on the temperature rating, quality level, and product weight.

  • 550-650: $100-$300
  • 650-750: $200-$400
  • 750-800: $300-$500
  • 800+: $500-$1000
Fill Power Affects Price(Jackets)

Fill power really doesn’t affect jacket price all that much. Down jacket price is almost entirely dependent on the temperature rating and product weight. Of course, warmer and lighter jackets will usually be more expensive.

Plan on spending between $100 and $300 on a quality down jacket. Remember that going with higher fill power doesn’t always make your jacket warmer.

Fill Power Does Not Tell You How Warm a Jacket Is!

Just remember that fill power doesn’t tell you how warm a jacket or sleeping bag will be. There are too many other factors to consider that affect warmth. It really depends on how much down is in the jacket/bag and how much room there is for loft.

When Does High Fill Power Make Sense?

Of course, premium down will have a serious price tag. High fill power down is used to keep jackets lightweight and easy to pack down. So the only time you really need 750+ down is when you’re trying to save space and weight in your pack or want a sleek winter jacket.

If weight and bulk really isn’t all that important you might as well save some cash and purchase a puffy jacket with low quality down. 100 grams of low quality down will always be warmer than 30 grams of premium grade down.

Comparing Down Quality

In theory, 80 grams of 450 Fill Power down will be about the same warmth as 40 grams of 900 Fill Power down. The premium 900 FP down will be about half the weight and size when compressed.

This is going to be hard to figure out because very few companies report how much down they use. Plus no formula is going to account for differences in down distribution and differences in jacket quality.

Fill Power With Synthetic Jackets

Each brand of synthetic insulation is going to have its own unique characteristics. Unlike down, there’s no easy way to test the warmth and compressibility of synthetic filling. You can’t really compare the insulation efficiency of synthetic and down products.

Refer to Sleeping Bag Temperature Ratings

When it comes to sleeping bags, fill power really only affects the weight and compressibility of your bag. Instead of looking at Fill power check out the bags temperature rating. Nowadays, temperature ratings are independently tested in a lab setting so they’re extremely accurate.

You might want to check out my post explaining sleeping bag temperature ratings.

Higher fill power really only explains why one sleeping bag with the same temperature rating weighs less than another. The lighter bag will also pack down smaller since it uses higher-quality down.

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