How much down in a winter sleeping bag?

I'm going to make a winter sleeping bag and am having trouble finding out how much 800 fill down I should put in the bag. The bag will be around 80" long and 40" across at the longest point. It will be a mummy style bag.

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  • 1 decade ago
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    I have sewn down sleeping bags in the past and used a number of different bag combinations for winter and mountaineering for over 30 years. A true winter bag (sub-zero rated) typically takes 2 to 3 lbs of high-loft fill. I have a question: first off, did you really mean that your bag would be 40" wide? 40" across would be far too wide to be a "mummy bag" and 40" in circumference is too narrow for anyone but a small child. Also, more important than any volume or weight of down is the design of the shell and baffles which allow the down to expand to create the insulating air space. This is a complex sewing problem. I'm a very skilled seamstress and have designed and built lots of different types of gear but would be very reluctant to do a sleeping bag from scratch (the ones I have sewn were from pre-fab kits from Holubar, Frostline and Altra, all of which are no longer in business.) They were incredibly complicated in construction and assembly.

    Are you planning to do this to save money? I think in the long run you will waste money on a project such as this. If you truly plan to sleep outside in the winter you can't risk bag that won't keep you warm. Constructing a shell that will maximize loft is really tricky. For around freezing you need at least 4 inches of maintained loft above you. Down to 15 to 20 degrees F you need around 5"or 6". If you might encounter 0 degrees F or lower, you might need up to 7" or 8".

    I have a more economical and practical suggestion, one that I have proved in years of winter camping. Buy yourself a moderate temperature rated down mummy bag (rated for around 20 to 25 degrees F). It should weigh around 3 # total or less and stuff down about the size of a large bread loaf. Then buy a slightly larger (tapered rectangular or modified mummy) single-layer polyester fill mild weather bag that will fit OVER the mummy bag. One of these should weigh in at 2 to 3 # and also pack down just slightly larger than the mummy. I have one that doesn't even have a zipper (to save on weight.) Using 2 bags together has a number of advantages:

    1. two small packed bags are easier to pack than one big one (and even a down cold weather bag will be bulky and weigh 4 to 5 # or more)

    2. you will be warmer with the down bag inside the fiber bag than in any single down bag.

    3. the fiber fill bag will resist moisture and protect the down bag from getting damp from condensation inside the tent --always a danger in the winter.

    4. you can tuck clothing between the two bags to add insulation and keep the clothes warmer and dryer.

    5. If the weather gets warmer you can wriggle out of the outside bag and lay on top of it with your down bag. Also, a polyfill bag gives you better insulation underneath than a down bag because your weight doesn't compress the fill as much.

    6. The overbag keeps your down bag cleaner, saving drycleaning bills or the wear and tear of machine washing.

    7. You will be able to use the poly bag alone in the summer (especially for canoe trips or any time the bag might get soaked) and also as an emergency bivy bag to take on day hikes and summit climbs. You can even use it as a sitting pad in the tent or outside in the snow. You can use the down mummy alone on Spring and Fall trips.

    I have used this system for 20 years and much preferred it to lugging my 5 # 6 oz. hand-made down mummy bag on winter trips. That bag was warm, but lacked versatility and was often too warm.

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  • Anonymous
    4 years ago

    For a cold weather bag I feel Marmot makes the best, just replaced my 15 year old Marmot 0 degree down bag I probably slept in 1,000 nights or more with a Marmot Col Membrain -20 degree 800 downfill. Have always found the Marmot temperature ratings to be accurate. That being said during the summer I carry a down blanket rated at 20 degrees, called a "Haven", made be Therm-O-Rest. I didn't like the original design and modified it to truly be just a blanket, weighs 19 ounces and is comfortable without any additional blankets/clothing to about 30 degrees, sleeping on an inflatable 2 1/2 inch Exped Synmat-7, weight 16 ounces. Pretty sure this is the lightest combination on the market. I've found I'm usually warmer without cotton between me and the sleeping bag, use a fleece material if you have to use anything. Any material will hold moisture against your skin inside the bag.

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  • Anonymous
    1 decade ago

    It'll depend on how much cold the user will be exposed to. If you're going to use it where the surrounding temperature gets to 40 degrees, you'll need a lot less fill than if you use it in temperatures around twenty below. Don't forget that a lot of the insulating factor depends on the loft of the fill, and upon what's between the sleeper inside the bag and the ground. Your best bet is to talk to a professional manufacturer or find an article in one of the popular outdoorsmen's publications on how to make them. Several such publications have a database that can be searched online...and they post the link to that database in each issue of that publication.

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  • Anonymous
    1 decade ago

    For a 0 degree down bag it's going to require 4" of loft on top, and less on the bottom so you'll have to essentially make two calculations, one for the l x w x h of the top/sides and one for the l x w x h of the bottom area. Next you take those measurements and divide by 800 to determine how many ounces of down you need to buy and then add 10% because that much can be lost in the process. Another secret is to only work with the down inside a tent set up inside your house to avoid it getting EVERYWHERE!

    And read both these pages:

    http://thru-hiker.com/projects/down_quilt.php

    Thru-hiker sells the raw down by the ounce if you don't have a supplier.

    http://www.backpacking.net/makegear/make-down-quil...

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  • 1 decade ago

    Why not just buy one? It will be built better and it will already have the temperature rating on it.

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  • Anonymous
    1 decade ago

    6 - 8", just what other mfg. are doing

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