The math around fill power and loft and jacket comparison.

[Kevin Burton]

So I'm comparing differing down jackets and trying to compare jackets with different fill weights and different fill power.

So I obviously can't compare them head on because it's apples to oranges..

So I need to normalize them.

well "Fill power is the number of cubic inches occupied by 1oz of down (uncompressed)"

… let's take two jackets:

Montbell Ex Light Down Jacket:
http://www.montbell.us/products/disp.php?p_id=2301344
fill weight: 1.8oz
fill power: 900
fill volume(cubic inches per oz): 1620

MontBell UL Down Parka:
http://www.montbell.us/products/disp.php?p_id=2301156
fill weight: 2.5oz
fill power: 800
fill volume(cubic inches per oz): 2000

… so this would hint that the MontBell UL Down Parka is superior as the fill volume is 2000. However, it has a hood so it's kind of an unfair comparison.

This seems to be a correct strategy though. For two jackets which both have hoods (or lack them) the one with the higher fill volume would be the way to go.

Actually price per fill volume would be another solid metric.

One issue is that other vendors do not publish their fill weight. Which means I can't do a comparison against Montbell, which DOES.

It makes me want to buy Montbell exclusively. The one issue I'm having is I can't find the Montbell Mirage in medium anywhere.

[Jerry Adams]

Possibly the clo/inch is different for different fill power but I have no idea which is bigger or by how much. That could effect your calculations.

The inner and outer lining provide a little warmth. With jackets that have so little down, this is more of a factor.

Lower fill power is supposed to resist humidity more, so the 800 FP might be better in real world conditions.

I have heard complaints that the Ex Light down jacket has so little down in it that it doesn't produce very much warmth. I forget where.

BGT has some reviews that might be useful http://www.backpackgeartest.org/reviews/Clothing/Jackets/

[Kevin Burton]

yes… you would have to factor in the amount of cloth too. However, in terms of heat, I don't think it's giving you much.

Maybe take in the total weight of the garment too.

The Ex Light down jacket definitely wasn't as warm for me.

Also, I was reading that the higher the fill power the more fragile it is… so while it's lofty and warm when you first buy it that might change a bit rapidly.

perhaps 800fp is superior in that it might last longer (so reducing the cost of the jacket).

[Dan @ Durston Gear]

Your approach is generally a fair one to use. I think it's far better than crude measures of loft. There are minor issues, such as hoods as you mention and differences in cut, sizing, distribution etc. Higher fill power down is more susceptible to losing loft from humidity, but I don't think it's necessarily shorter lived.

And yes the Mirage is awesome. If you find it in medium please order 2 and send one to me.

[Kevin Burton]

I created a spreadsheet with all this data:

https://docs.google.com/spreadsheet/ccc?key=0AkBAy3nnEh65dEtpNlpzSXJpa0NLMDNlZFZpa1I1Wmc&usp=sharing

I only added the down jackets that looked like ones I would buy.

Montbell is the only vendor that you can do this with. None of the other vendors publish their fill weight. So they're not getting my money.

Though with the Montbell data it seems you can multiple the weight * 0.35 (approx) to get the fill weight.

The EX LIGHT DOWN JACKET MEN seems to be more than 2x some of the other jackets in terms of fill volume.

This data REALLY does make the Mirage look amazing.

The only thing that makes it more confusing is whether 800 fill power is a better investment as 900 fill power is more fragile and degrades quickly. I would need some sort of data to determine how quickly it degrades to 800 fill power.

[Dan @ Durston Gear]

BPL collected data on the down fill of quite a few jackets in the State of the Market Report a couple years ago. You can view that here and add these to your spreadsheet:

http://www.backpackinglight.com/cgi-bin/backpackinglight/ultralight_3-season_down_jackets_sotm_2010_part_2.html#.UwIPe3lIjfY

Montbell also makes the "Guide's Parka" which looks like the same thing as the Frost Smoke but without the more durable fabric patches, so it should offer a higher down %. It's not officially offered in N. America but you can find them on eBay:

http://www.ebay.com/itm/New-Mont-bell-Men-Ultra-Light-Down-Conseal-Zip-Guide-Parka-1101384-S-M-L-XL-s-/231156565003?pt=US_CSA_MC_Outerwear&hash=item35d201440b

[J-L]

Backcountry Gear has the Montbell Mirage in Medium (says Dark Navy ships in 24 hours).

[Kevin Burton]

I found it at a local store in stock in medium.

http://www.downworks.com/downworks/Welcome.html

They have 3 other jackets in stock in medium in the three other colors but I got the last gunmetal grey :-P

… so I guess if you want one call these guys.

and it was $309 so the normal pricing. But I guess it's in CA so I had to pay taxes on it (boo!)

[Franco Darioli]

"Montbell is the only vendor that you can do this with"

Maybe I am reading this the wrong way but for example Western Mountaineering does post the fill weight of their jackets.
The fill on Quick Flash is around 2.5 oz, the hooded version has 3oz.
Fill weight is also listed for their other (heavier) jackets.
Feathered Friends list the fill weight of theirs as Sierra Designs also does.
For example the 14oz SD Stratus Jacket has 3.5 oz of fill.
(those are the only ones that I looked up…)

[Kevin Burton]

> Western Mountaineering does post the fill weight of their jackets

see… this is why I avoid using superlatives.

the vendors I picked all were not using fill weights. Kudos to Western Mountaineering!

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