Another Down Jacket Question(s)

9:49 a.m. on February 29, 2016 (EST)
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Hi all,

Firstly hello, secondly apologies if this has already been asked or if the answer lies elsewhere but I couldnt find anything so I thought I would ask and hepefully either find out or get sent in the right direction to continue research.

1) I have been told that fill weight can be as important as fill power ie a larger weight of lower FP can be as warm as less weight with higher FP but is there a chart or formula that gives some kind of comparison? I appreciate there are a lot of other factors in play such as construction etc but in a perfect world how do you start to figure out the likely warmth/relative of different fill powers and weights. wil 210g of 800FP be warm/ how much 550FP down would you need for the same warmth etc.

2) Given that down performs badly when wet; I have a completely non waterproof/resistant and untreated down jacket that I often find cold in relatively warm weather. Is this likely to be moisture in the air on wet days affecting it? The coat is not wet or rained on its just so non resistant this is the only thing I can think is in play. Any thoughts? Thanks for you help

11:03 a.m. on February 29, 2016 (EST)
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You can sort of work out an idea of the fill vs weight comparison by looking at sleeping bags that are rated the same temperature. An example I found listed a 20° bag using 850 fill weighing 29oz versus a 20° bag using 550 fill and weighing 41oz. This isn't an exact science because other materials vary as well, but that is about 40% more weight to use the lesser fill to reach the same comfort level, at least  on the label.

Sensitivity to moisture increases as you move up in the quality scale. A little moisture can really sap the fluff out of 850 fill while the same amount wouldn't cause as much of a problem for a lesser grade of down. Won't guess as to whether that is what you are seeing with your jacket though, as there are too many other factors involved.

Lastly, hello and welcome to Trailspace!

7:27 p.m. on February 29, 2016 (EST)
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The key to insulation is loft. Fill power is a measure of cubic inches per ounce, so basically how much loft you can get out of a given amount of insulation weight. To turn it around, a given amount of loft will generally provide a certain amount of warmth, so the higher the fill power the less weight of insulation is required to achieve that given amount of loft.

You can't just calculate the down's fill power and weight against each other to come up with a warmth rating, it also depends on baffle construction, where the down is distributed, and other factors.

As for a jacket feeling cold on warm wet days that's hard to say, depends again on a variety of factors like the jacket's shell material, just how damp the air is, how long you're out in it, and so on. I would think the down would have to start getting damp inside the jacket before you noticed any difference.

2:08 p.m. on March 4, 2016 (EST)
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i agree with the comment about loft.  that's the best way to figure out how warm a jacket will be, and it's a function of not only the insulation, but also the way the insulation is encased.  for example, virtually all lighter-weight down sweaters and jackets are sewn through, the insulation is encased between the inner and outer shell material.  that limits, to some degree, how much the insulation can loft.  warmer down jackets, intended for colder temperatures (and costing more) have baffles sewn in between the inner and outer shell layers.  baffles allow the insulation to loft more, provided the jacket has enough insulation to do that.

example - my old mountain hardwear sub-zero jacket has 650 fill power down.  not the lightest or fluffiest.  however, it has a massive amount of down, and the torso of the jacket is baffled.  if you're otherwise properly clothed, this jacket is good into the -20/-30 f range.  whereas, i have a newer mountain hardwear phantom, 800 fill power down, that's good to zero or maybe -10.  the phantom is a sewn-through jacket, no baffles.  it's also shorter at the hem.  both have good insulated hoods.  But....the sub-zero weighs 25 ounces, and the phantom weighs 16.  

i'm not sure why a down jacket would work less effectively in cold weather, damp or not, unless the damp air is somehow collapsing the down insulation.  you would know - down gets heavy and clumpy when that happens.  could be the jacket is too warm, that you're sweating more as a result, and that you're getting chilled from sweating too much.  i have seen that happen on trips when people don't de-layer on steep uphills in the winter.  

my lighter down jackets claim to have some kind of water repellency, but my experience has been they aren't a good layer to wear in damp/wet weather.  i have never had a down jacket fail because it's humid, though.  

January 29, 2020
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