Down feathers, how birds keep you warm

A bird’s down is a layer of fine feathers located beneath the tough exterior feathers that help keep it warm.

Those down feathers can keep you warm, too, if you buy a sleeping bag or coat that uses them for insulation. The loose structure of the feathers traps air, which helps insulate against heat loss.

In the United States, any product labeled “100% Down” must contain only down feathers. In contrast, products labeled “Down” can contain a mixture of fiber and feathers. Also, products labeled as “Goose Down” must contain at least 90% goose down, 10% goose feathers.

Down insulation is rated by fill power, which is the number of cubic inches displaced by a given ounce of down (in3/oz). Eider-down has the highest fill power, at 1200. However, even down with a fill power as low as 550 still provides reasonably good insulation.

Higher fill-power downs insulate better than lower fill-power downs of the same weight.

Most sleeping bags and coats range from about 400 to 900 fill.

Down rated 500–650 fill is warm enough and light enough for most conditions.

Down rated 800–900 fill is very lightweight and suitable for frigid weather.

Cared for down will retain its loft up to three times longer than most synthetic fill; however, there are downsides:

1 – When down gets wet, the thermal properties are virtually eliminated.

2 – Down forms clumps when wet and will mildew if left damp.

3 – Down will absorb and retain odors.

4 – Most down is collected after the birds are killed for meat, but in a few countries like Poland, Hungary, and China, the live-plucking of birds still takes place. The cruelty of this method should not be tolerated, so buy from companies that do not support this or by a synthetic fill.

A damn good sleeping bag

I’ve been hiking in the winter cold all day; It’s almost dark, and the world I left behind is in chaos. The grid’s been down for three weeks; and my neighbors, well they all turned on me when they found my supplies. I just barely got out of there with my life, and I’m too tired to build a fire. All I want to do is sleep, and I can do that because I bought a damn good sleeping bag.

A good bag is a lifesaver when you’re on the move. Having one means you don’t have to start a fire when it’s cold and wet. Just set up the tent, get inside, dry off, and crawl in.

There are three primary types of sleeping bags

Winter bags typically come with temperature ratings of 0°, -20°, and -40° degrees.

Three season bags are the most popular and vary in quality. Fortunately, low quality and high-quality bags cost about the same, so spend the extra money for a good one. Temperature ratings for these bags also vary, but I would not get one rated higher than 20° degrees. Remember your buying a survival bag, and your doomsday can hit any time of the year.

And finally, summer bags are typically lighter but have higher temperature ratings.

What’s Inside Matters

What’s inside the bag matters too, and there are two basic choices, goose down and synthetic. The main thing to remember is, goose down will be lighter, less bulky, and warmer as long as it’s dry and synthetic will be heavier, but will still keep you warm when wet.

The best “rule of thumb” to use when deciding on which bag to buy is to add 10-15° degrees to the actual temperature rating; for example, you should always assume a sleeping bag rated to 20° degrees, will only work to temperatures of 30-35° degrees.


Their shape is also important. A mummy bag is form fitting and holds heat well, while a square bag allows you to move around in it at the expense of heat loss. There are also other shapes that work well, and some bags have sleeves built into them to hold a sleeping pad.

Other Options

There are other options you can get with a sleeping bag that you may or may not feel you need: right or left side zipper, inside pockets for example.

Just Remember

It is always better to have a bag that is a “bit too warm” than “not warm enough,” when it comes to your survival on a cold winter night.