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 Post subject: Down fill calculations
PostPosted: Mon Sep 21, 2015 5:03 am 
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I'm shopping for a down jacket. It's often hard to compare the warmth between 300g of 700 fill, 200g or 850+ fill, etc.

I was wondering if anyone had a good chart with comparative data so I can start off this and code a calculator. I'll throw the calculator on FOXTAC for everyone's benefit.

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 Post subject: Re: Down fill calculations
PostPosted: Mon Sep 21, 2015 5:49 am 
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Couldn't find anything via my schools library. I'll ask my friend at work if she knows of any open source stuff that has some info about it.

Anyway, what you'll end up with is just a generic science calculator that doesn't tell you anything about the products actual performance... The reason for this is that seams and such affect the insulation, so if one 800 fill jacket is covered in seams (or even worse has the baffles that are separated by a stitchline), it might not be warmer than a 550 fill that has no outside seams. I would debate that construction plays a bigger part than most people think.

Also the design and placement of baffles matters. You could in theory have a product that has shitty baffle placement that insulates in areas where you don't need insulation at all... But if you do place it in the right areas, you'll be *drumroll* warm.

So yeah... I don't see the point of a calculator to be honest. A sweating manniquin test would probably be the closest you can get to some results that are worth anything, even though they won't address the placement of baffles and just the overall insulation.

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 Post subject: Re: Down fill calculations
PostPosted: Mon Sep 21, 2015 6:23 am 
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Yeah I'm aware of the differences in baffle size & shape, seams placement, sewn-thru, face/inner fabric breathability/windproofness, etc.

It's just an additional tool that, despite being imperfect, will be a much better indicator to compare them than just reading manufacturer's descriptions.

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 Post subject: Re: Down fill calculations
PostPosted: Tue Sep 22, 2015 1:58 am 
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Asked my friend, no luck.

I honestly don't think even manufacturers know what the end result will be in most cases..

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 Post subject: Re: Down fill calculations
PostPosted: Tue Sep 22, 2015 2:30 am 
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Quote:
Technically speaking fill power is a measurement of the amount of space one (1) ounce of down (as shown in the cylinders below) will occupy in cubic inches when allowed to reach its maximum loft.

For example, one (1) ounce of 800 fill power goose down will loft to 800 cubic inches. The higher the fill power the larger the down cluster. Larger down clusters will loft higher; sleep softer, last longer and sleep warmer.


http://www.downandfeathercompany.com/ho ... power.aspx

Quote:
The 3D structure of the down clusters creates "loft" that traps air. The greater the loft, the warmer the insulation. "Fill power" is a measurement of that loft. This is accomplished by measuring how many cubic inches an ounce of down displaces when allowed to expand to its fullest. If an ounce of down takes up 500 cubic inches of space, then it has a 500 fill power; 700 cubic inches equals 700 fill power; and so on.


http://www.ems.com/ea-understanding-dow ... ation.html

That's a good part of the answer.

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 Post subject: Re: Down fill calculations
PostPosted: Tue Sep 22, 2015 4:29 am 
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So how would you use that info to decide which jacket is warmer of the 300g of 700 fill or the 200g or 850 fill?

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