Fluff vs. Stuff: A Simple Guide to Sleeping Bag Warmth

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Fill Power vs. Fill Weight: What It Means for Your Sleeping Bag

When shopping for a sleeping bag, you’ve probably come across terms like fill power and fill weight. These are key factors in how warm and packable your bag will be—but they can be a little confusing at first. Let’s break them down in plain language so you can choose the right sleeping bag for your adventures.

What Is Fill Power?

Fill power measures the quality and loftiness of the down insulation in your sleeping bag. It’s a number that tells you how much space one ounce of down can fill. The higher the number, the fluffier (and more insulating) the down. The same rule may be applied with synthetic fillings, although they are rated differently and fill power is specific to down.

Quick breakdown:

• 600 fill power: Standard quality

• 700 fill power: Better warmth-to-weight ratio

• 800+ fill power: High-performance, ultra-light, and super warm

Higher fill power = warmer, lighter, and more compressible.

What Is Fill Weight?

Fill weight is the amount of down (or synthetic insulation) in the bag, measured in ounces or grams. More fill weight generally means more warmth—but only when compared within the same type of insulation and fill power.

So a sleeping bag with:

• 800 fill power and 10 oz of down might be warmer than a bag with

• 600 fill power and 12 oz of down

In other words: It’s not just about how much down is in there—it’s about how well that down fills the space inside the bag. As the fill power rating rises, you get a higher quality, loftier fill that provides better insulation. It's worth noting that synthetic insulation does not compress as well as down, and its performance can be affected by moisture. However, in general, a higher fill weight will provide more warmth.

Why Both Matter

Think of it this way:

• Fill power = quality of insulation or loft per gram

• Fill weight = quantity of insulation or grams of fill

You need to look at both numbers to get a sense of real-world warmth. Together, they tell the full story about how warm, light, and compressible your sleeping bag will be. And when we refer to quality here, it doesn't mean a superior class of feathers - it's referring to the loftiness - So, the more fill, more loftiness, more quality.

Duck Down vs. Goose Down (and What's Up with Grey vs. White?)

However, not all down is created equal—and not all of it comes from the same bird. 

Goose down generally has larger, loftier clusters than duck down, which means it can achieve higher fill power and insulate better with less weight. That’s why you’ll often see premium sleeping bags using goose down, especially in colder-weather models. Duck down, while only slightly less lofty, is more affordable and still offers excellent warmth—especially at mid-range fill powers.

White down vs. grey down - Believe it or not, the color makes zero difference in performance. Manufacturers often prefer white down in lighter-colored fabrics to avoid it showing through, but functionally, grey and white down insulate the same. So don’t let color sway your decision—it’s just bird fluff at the end of the day.

Choosing the Right Sleeping Bag for You

Here are a few quick tips:

• Backpacking in mild weather? Go for a lighter bag with mid-range fill power (600–700).

• Cold-weather camping? Look for higher fill power (750–900) and higher fill weight.

• Trying to pack ultralight? Choose high fill power—this lets you carry less weight without sacrificing warmth.

Bonus Tip: Also Consider the Temperature Rating

Most sleeping bags also list a temperature rating (like 20°F or 0°C). This is based on lab testing and gives a ballpark idea of how cold it can be before you’ll get uncomfortable. Just remember: personal factors like metabolism, sleeping pad, ground cover, moisture levels in the air, and clothing also affect how warm you’ll feel.

The comfort temperature is the lowest temperature at which an average cold sleeper will feel comfortable, while the comfort limit is the lowest temperature at which an average warm sleeper will feel comfortable.

In summary: To choose the right sleeping bag, look at fill power, fill weight, type of filling, and the temperature rating—they all work together.

Backpack Her World - Sleeping Bag Comparison Chart

	Name Color	Description	Fill Power	Fill Weight	Comfort Temp. / Comfort Limit	Fill Type	Features
	Kamperbox SC900 BLUE	lightweight thin mummy	760 g	900 g	55°F / 47°F	Synthetic Cotton	Inside Pocket, Machine Washable, Water Repellent, Windproof, Rip-Stop Outer, Heavy-Duty Double Zipper
	Kamperbox DD800 BLUE / YELLOW	Super Lightweight, Warm, Thin	800+ g	500 g	50°F / 41°F	90/10 Duck Down	Open Top, Convertible Mummy
	Kamperbox Cozy DD300 GREEN	Thick, Warm	400 g	890 g	32°F / 24.8°F	80/20 White Duck Down	Inside Pocket, Mummy, Heavy-Duty Double Zipper, Water Repellant
	Kamperbox Cozy DD600 BLUE	Thick, Warm	630 g	1100 g	26.6°F / 19.4°F	80/20 White Duck Down	Inside Pocket, Mummy, Heavy-Duty Double Zipper, Water Repellant
	Kamperbox BubbleAir 2 BLACK	Ultralite, Thin	550 g	1 kg	50°F / 32°F	90/10 90% Duck Down	Open Top, Convertible Mummy,
	Kamperbox SD1100 RED or BLACK	Ultralight, Thick	1100 g	1800 g	14°F / 5°F	Synthetic Down	Mummy, Waterproof, Hypoallergenic, Machine Washable
	Kamperbox GD1000 DARK GRAY	Lightweight, Thick, Warm	1000 g	1.7 kg	5°F / 0°F	90% Goose Down	Mummy, Winter, Cold, Waterproof, Windproof
	Kamperbox GD1000 Splicer BLACK	Lightweight, Thick, Warm	1000 g	1.8 kg	0°F / -10°F	90% Goose Down	Mummy, Winter, WaterproofExtreme Cold, L + R Zipper Option (can zip 2 bags together for one larger person or couple)