Amount of down…
Posted: 25 September 2009 05:19 PM   [ Ignore ]  
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I’m wanting to make a down blanket that one of my dogs (2 labs) can carry, and could use some clarification on the fill amount.

It says 3 oz. covers 800 c.i.

So…if I want a 6ft x 3ft blanket with 2 inches loft, that would be 72x36x2in = 5184 cu in?

That would mean I would need 5184/800=6.5 bundles of 3oz down? That’s getting spendy for a little blanket. is this correct?

I suppose I could make it, say, 5 ft and only one inch thick. 2 inches may be a little warm for them. Your thoughts?

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Posted: 25 September 2009 05:55 PM   [ Ignore ]   [ # 1 ]  
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Hi Paul,

Your calculation is correct right up until the last step where you mix up ounces of down (6.5) with 3 oz of down (the way it’s sold).  Your calculation is telling you that you need a little more than two bags of down.

Note that it’s a good idea to overstuff by 10% or more. 

The full calculation:
a) determine volume: (72” x 36” x 2”)=5184 cubic inches
b) calculate fill: 5184 cubic inches/800 cubic inches per ounce = 6.5 oz fill * 1.1 for overstuff = 7.2 oz required /3 oz per bag = 2.4 bags.  Round up to 3 bags required.

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Posted: 29 September 2009 05:37 PM   [ Ignore ]   [ # 2 ]  
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Thanks, Ayce. Do you know roughly the temperature rating of the loft thickness of down? For instance, if I make a blanket 1 inch thick versus 2 inches thick, what would be the rough rating between the two?

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Posted: 29 September 2009 07:04 PM   [ Ignore ]   [ # 3 ]  
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1” is summer, 2” 20’s/30’s

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Posted: 30 September 2009 08:52 PM   [ Ignore ]   [ # 4 ]  
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This might be useful in estimating the down loft for a sleeping bag, quilt, or blanket. Taking the down loft reported by Western Mountaineering for their bags and halving it for a 1-layer loft height, the down loft height for a given temperature in Fahrenheit would be:

Loft” = 3.5 - 0.05 * F   (See graph below)

Most of the WM bags use a very lightweight ripstop (I believe is similar to the T-Hiker’s momentum but AYCE could verify). I wouldn’t go too far with the formulae in the high temperatures (e.g. over 70 F).  The material layers play a much greater role at such low loft heights.

I hike in the Southern Appalachians a lot and the temperatures in summer are considerably different than either the dry climates of the West or the northern Appalachian mountains.  Low temperatures in the 50s to 70s are common in the summer at elevations less than 5500’.

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Loft Height versus Temperature.PNG
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