Down Comforter Warmth Comparison Calculator
Down comforters and sleeping bags are great because they offer unmatched warmth and also great breath-ability. Though I am speaking about comforters, all the information in this article is also applicable to down sleeping bags and other down products. One way in which down comforter warmth is measured is the fill power of the down. This is actually a bit misleading, as the fill powder is not a measure of warmth, but a measure of volume.
The fill power of down does affect the warmth of a comforter. The more volume there is, the more warm air the down can trap, creating a warmer bedding. Along with the fill power of the down itself, you must consider how much down there is in the comforter and how spread out the down is. Once you have all this information you will be able to judge how warm a don comforter (or any other down product) is.
How Down Keeps You Warm
Down keeps you warm by creating air pockets between the down feathers. These pockets of air trap warm air as it rises from your body. This warm trapped air is stuck next to your body, keeping you warm.
Down which has a higher fill power has more of these air pockets per ounce. This is why many people assume that higher fill power always means a warmer product.
The more down in a product the more air pockets are created. A heavier down jacket, sleeping bag or comforter is going to be warmer than a lighter down product, all else being equal.
Estimating the amount of air pockets in the down provides a good idea on how warm the down will be.
The Eye Ball Method For Measuring Down Warmth
The easiest way to measure the warmth of a down product is to look at how much loft and volume there is. The more fill inside of the product, the warmer it will be. A thick down comforter is going to be warmer than a thin down comforter. This is because thickness means more air pockets where warmth gets trapped.
If you are comparing two different down products, take a look and see which one is thicker. The thicker one is almost always going to be warmer.
When shopping for a down comforter, look at the thickness of the comforter. Be sure to check the thickness at all locations. Check the top, bottom and middle of the comforter for how thick the comforter is in each location. Cheap comforters have down that shifts around, creating pockets or warmth and pockets or cold. You want to avoid this by getting a high quality down comforter which uses baffle box construction.
Ray Jardine Formula For Measuring Sleeping Bag Warmth
Ray Jardine is an American rock climber and one of the first two people to free climb the west face of of El Capitan in Yosemite. He's an outdoor enthusiast, taking part in many sports. He also developed a formula for measuring sleeping bag warmth. It's a fairly crude formula and doesn't work very well for very warm and very cold sleeping bags, but is still a nice estimate of sleeping bag warmth.
The formula is:
Warmth = 100 - (40 x T)
Where T is the thickness/loft of the sleeping bag, in inches. The loft of the sleeping bag should only measure the top of the sleeping bag that will be covering the person, as the bottom of the sleeping bag does not provide much warmth.
The above formula provides an estimated warmth, in Fahrenheit.
This is a better measure than just eyeballing the thickness of a down product. With this formula we now have an actual degree estimate of how warm a down sleeping bag will be. This same formula can be used for down comforters.
Use this Jardine formula calculator to get an estimated warmth of your sleeping bag:
Sleeping Bag Warmth: F
Again, the Jardine formula doesn't work for very thick or very thin sleeping bags.
More Accurate Down Warmth Calculator
To get a more actuate measurement of how warm a down comforter or sleeping bag will be, you need to know a few different values. Luckily, most down comforters clearly tell you these values.
First you need to know the fill power. This is the volume per ounce measurement and most down products have this clearly advertised. You also need the weight of the comforter or item you are looking at. Finally, you need the dimensions of the comforter; that is, the height and width of the comforter.
Using all of these numbers you will be able to find out how much warmth a comforter provides, and compare it with other down comforters. Using these calculations you can see which down comforter is warmer.
Make sure you have filled out each box to get a true comparison of the two comforters.