Down Fill Power Explained

If you’ve ever compared down products, chances are you’ve come across various rating terminology. But what do they actually mean? And how does it impact how warm and cozy you’ll be on a chilly outdoor adventure? Read on to find out!

Sara Hall Avatar
Written by: | Reviewed by: Kieran James Cunningham
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When a winter wonderland is calling you out to explore, staying warm shouldn’t be the reason keeping you cooped up indoors. With a little help from our feathered friends, you can enjoy wintertime adventures as much as those in any other season.

Down, whether used in jackets, sleeping bags, or slippers, will warm you up without weighing you down. It’s a natural insulator that works better than any synthetic alternative. But before you go buying any puffy gear, it’s wise to first learn what to look for. To that end, we’re here to help!

Fill power is an important feature to consider with any high-quality down product, and if you’re wondering why that is, keep reading! Knowing this information will help keep the warm air in and the cold air out, ensuring you stay safe and cozy during any cold-weather activity.

All You Need to Know

A Primer on Plumage

Down is the fluffy plumage on birds underneath their outer layer of thicker feathers. It’s lighter than a feather, literally, and creates cozy insulation, giving it an unbeatable warmth-to-weight ratio.

While it’s not actually a feather, the dandelion-shaped groupings of tiny fibers called “down clusters” create the superior insulation outdoor adventurers know and love. In a down jacket, for example, the air pockets created by the clusters trap warm air and help retain your body heat. 

down feather
Down is the fluffy under plumage that helps keep birds warm. ©Kieran Cunningham/MyOpenCountry®

Working alongside other features like pit zips, it’s still breathable enough to ensure you don’t overheat while out hiking.

Commercial products are made from either goose or duck down. Both types are structured the same, but geese clusters tend to be larger and have a higher FP.

What Does “Fill Power” Mean?

The warmth of down products is dependent on both the down quality, which is measured by fill power, and the quantity of the feathers/plumage, which is measured by fill weight. 

Fill power measures the fluffiness or “loft” of the plumage. It refers to how many cubic inches can be filled by one ounce of down. Better quality feathers will have more loft (thus filling up more cubic inches of space) and result in higher FP. 

Ratings can range from 300 to around 950. Anything below 450 is considered low FP and above 550 is high quality. Clusters of 800 FP are roughly the size of a quarter.

Why Is It Important?

Higher down fill power products are ideal for wintertime adventures. Higher FP means greater loft, which can trap more air and create better insulation. This means the heat generated by your body will stay inside, keeping you toasty warm. 

Woman standing in sleeping bag in the snow
Higher FP provides more warmth with less weight and greater compressibility.

Lower fill means it won’t retain your body heat as well (but this can be countered – more on that in a minute!). High FP numbers result in warmer, but more expensive, products.

But the price tag might be worth it, depending on your needs. 

Outdoor adventurers love down because it compresses better than synthetic insulation. The higher the FP, the better it compresses. If you need to stuff your down jacket or sleeping bag into the smallest sack possible, a 900FP product will be more packable than a similar one with 650FP. Lower FP items tend to be bulkier and heavier as the product is making up for the low FP with more weight.

Fill Power vs Fill Weight: What’s the Difference? 

While fill power is how quality is measured, fill weight measures the quantity of down fill, calculating the actual number of ounces used in the insulation. More ounces of down means a thicker, warmer item. But, as previously stated, this also figures into how well your gear compresses. A higher FW usually equates to a higher packed weight and packed size.

hiker in down jacket drinking from thermos overlooking mountain valley
Balancing price against fill weight and power will depend on the intended use and your budget.

Both metrics are important to consider when selecting a product. Ideally, you need to find a balance between the two that works for you.

When Is High FP Needed?

Down jackets and sleeping bags are generally and justifiably deemed essential for any camper or backpacker who plans on having adventures during winter or the shoulder seasons. As explained above, the higher the fill power rating, the warmer you’ll be!

If your goal as an outdoor adventurer is to save weight and space, it will be worth the cost to pay for high FP. For example, a jacket with more ounces of a lower-quality down insulation (10 oz. of 550FP) could offer the same warmth as a jacket with a higher-quality feather but less fill weight (4 oz. of 800FP), but it will be heavier, bulkier, less packable, and offer a poorer warmth-to-weight ratio. 

Down Vs. Synthetic Insulation

Traditionally, the biggest benefit of synthetic insulation over down is its ability to retain insulation capabilities and warmth even when wet. The drawback is that synthetic insulation usually has a poorer weight-to-warmth ratio. That means a synthetic-fill jacket, for example, needs to be heavier to reach the same level of warmth. 

Nikwax hydrophobic down logo close up
Many brands apply a hydrophobic coating to down to help them stay dryer. ©Kieran Cunningham/MyOpenCountry®

Most high-end brands now use a DWR (durable water repellent) finish to help you shake off slightly wet weather (not a rainstorm). Others use a hydrophobic coating, which covers the feathers in a chemical so they absorb less water and dry faster.

What Is the Down-to-Feather Ratio?

The fine layer of soft feathers underneath the tougher exterior feathers of a bird is what’s used in down products. The rigid feathers on the outside can add durability to firmer feather-filled items, while the softer and more delicate plumage underneath can add warmth and comfort when coziness is key. 


The down-to-feather ratio determines how much of each is used in a product. To ensure the best insulation, you’ll want a ratio of 90% down and 10% feathers (written out as 90/10). 

You’ll still get high-quality products with 80/20 or 70/30 ratios, but the fluffier the better. Because down is loftier, it’s better at insulating than the tough, exterior feathers. A higher percentage of down fill simply means a warmer (and lighter) product. Again, however, this is usually reflected in the price tag. 

What is RDS?

The Responsible Down Standard ensures that feathered-filled products come from certified farms that meet certain objectives and standards regarding animal welfare. RDS materials come from ducks and geese that have not been subjected to any unnecessary harm.

female hiker wearing down jacket
Many of the higher-end brands use RDS down.

A key point for RDS is the “holistic respect” of the birds’ welfare throughout their life at the farm. Live-plucking, molt-harvesting, and force-feeding are all prohibited. 

RDS also confirms the chain of custody as materials are processed at the farm and delivered to the supplier for the final product. 

High Down Fill Power = Maximum Warmth & Compressibility

All told, the bottom line is as follows: the fluffier, the better. The higher the FP, the better quality the insulation and warmth-to-weight ratio will be. 

But, if you’re adventuring on a budget, there are other things to consider, such as fill weight, down-to-feather ratio, weight, and compressibility. It all depends on your needs and what you’re looking for in your gear.

If you have any questions, feel free to ask away in the comment section below! And feel free to bookmark or share this post with anyone else looking to learn more about the topic!

Last update on 2024-06-20 / Affiliate links / Images from Amazon Product Advertising API

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Sara Hall Avatar

Sara Hall is a journalist, photographer, and freelance writer in her professional life, and is passionate about camping, hiking, and backpacking in her personal life. Growing up in the rural mountains of Northern California, a love of the outdoors was instilled in her at an early age.

Her favorite adventures are often solo backpacking treks out in the wilderness. Or hiking most weekends on local trails. Or with friends and family discovering new campsites. As long as she’s exploring, that’s her new favorite trip.

For Sara, one of the best moments of every journey is turning a corner or climbing above a ridge and an epic view reveals itself. That moment is one-of-a-kind and no two people experience it the same way. That’s yours and yours alone.

She also loves to travel and take local and long-distance road trips.

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