850 vrs. 900 fill down..

Very, very little difference. I suppose you could have them underfill by an ounce or two for the same loft, but……

The shell fabric you choose is significantly more important in this case.

Epic or Pertex Sheild EX what would you say the pros and cons are to either or?

The "fill power" has units of cubic inches per ounce. In other words, under the specified test conditions, an ounce of 850-fill down fills a volume of 850 cubic inches. So 900-fill down is about 6% more voluminous for the same weight. I've read a few opinions that 900-fill won't stay 900 for the long term, but I really don't know. Either one is very good down.

I think i get the concept..

Kinda weird FF the Holy grail of custom bags only offers one Material choice at this point. The Epic option is now only on old/previously made bags and fairly limited stock at that. Not to mention i only have two color options for my $750 plus tax and shipping bag. Ow well i am sold they make the best bag so i will take the leap!!

Down, especially good down, holds a lot of air in trapped cells between feathers. The difference between 850 and 900 is minimal but can be significant in cold weather. These are US ratings btw. EN ratings stop at 800, and take into account some insulating value of feathers (the difference between Eider and Goose.) Both may fill at EN800 but Eider will be warmer.

Anyway, high lofting down has a down side. It compresses really easily. The weight of the material can press it, soo, often these bags are only offered with a light shell. Overstuffing is often used to get around this. Slightly overstuffed(say around 5%) usually compensates. This doesn't make the bag any warmer, really. It just prevents collapse from a week in less than optimal conditions.

Much of a bag's loft at the high fill numbers is due to static electricity. Like the old gold leaf test, plumes with a static charge will open up. This means that to get the benefit of good high lofting down it needs to be clean…very clean. Laundering ounce per 2 weeks of use is probably about right. Because of the increased frequency of laundering, you do not need much down wash (a MILD soap.) About 1/2-1/3 as much as they say on the container. NO VANES in the washer. It will break baffles. Gentle handling after a three rinse cycle, to insure washing all traces of soap out of it. If you do this in a tub, roll it in some towels. Carefully, cradle as much as possible in your hands with fingers spread wide and don't drop it. Complete drying is next, usually as hot as your fabric will allow…(no heat, very low.) Down will handle the heat, OK. The shell will NOT. A light spritz of DWR every 2nd washing to keep out any drips. DWR treatment for the feathers seems to keep the static slightly longer than not. But, it does leave a slight residue on the down plumes. Not real sure on this one…

With 900 fill power (FP) down, you often start loosing some loft within a few nights of laundering. At the end of 15 days, it will likely need washing. Good down requires a bit more from the user. It will also deliver more in sleeping comfort. If the conditions are real cold, keeping moisture out of the bag, and ice, may be more of a problem than loft.

Very informative response thank you very much.

Kinda makes me think i might be better of with 850 long term?

This is an ongoing and open debate. Theory says go with 900 Fp down. Practice says go with 850. Like a good Ferrari, it goes like hell, but they always need a tune up.

Hi James,

I use various sleeping bags and garment with 900fp down and I did not relaise they need to be washed so often to retain loft.

Cheers,

Stephen

"I use various sleeping bags and garment with 900fp down and I did not relaise they need to be washed so often to retain loft."

I didn't either when I got my first down. I washed it twice per year, but it quickly started loosing it's loft. After looking into it, and researching it, I realized I was way behind what was actualy needed. After studying more about down I realized the loft was all important. Clean down lofts higher than unclean down. Part of that was elctrostatic stuff, part was oils clumping stuff. I started to wash it every couple weeks and fluff it every time I got back (low heat with tennis balls for a couple hours.) I was at least 5-7F warmer in the bag and I could easily tell the loft by looking after a couple washings and several fluffings. Launderd correctly, washing does not hurt down. Go easy on the soap, handle it delicatly and dry thouroughly. Many years later, I well agree that this is the way to go.

Hi James,

You speak of any compression as though it is a bad thing, and overstuffing as though it provides no additional warmth.

Richard Nisley on these forums has done extensive testing and proven otherwise – that overstuffing in most conditions up to about 2.5x "fully lofted" value still provides a linear increase in warmth, or compressing a fully-lofted down insulation by the same amount would retain its exact original warmth.

A person can probably expect too much from their down in terms of loft. It is probably as important to have 'enough' down in a bag as it is to wash it occassionaly. By emphasizing extreme loft too much, it is easy to underfill a bag. I ran across a story about Western Mountaineering recently in MAGAZINE OUTDOOR. Here's an exerpt;

According to Gary Peterson, WMs sales manager, what is called 900 fill-power down today would hardly have been called such 20 years ago.

"What was 700 fill power 20 years ago is similar to 900 today," Peterson says. " The product didn't change, they just added to the testing. "

The article goes on;

Where many companies would be happy to slap a 900 label on the product to impress the consumer, WM will not buy into the inflated system. As they refuse to cut corners on the quality of down, neither will they mislead the customers with what they believe is over-rated fill power.

"We buy 900 but call it 850+, he notes.

I think it was two years ago I did a study on compression. Compression ratios of 30:1, sometimes more up to 40:1, are possible by hand. This does not have any effect on a bags performance once it is removed and shaken out, given clean and dry down. This was based on a targeted audience of 54 backpackers using high lofting down from the backbackinglight e-mail list.

Generally I agree with Richard. Mostly, the lofting is not that important compared to the insulating effect of the feathers themselves. But I disagree that it has no effect. My 40F bag, for example is fine, extended down to 30F, with multiple layers I got cold. Reducing the layers by one, and I was *warmer*. Why? About 5 years ago I posed this question, and the vast majority agreed that it was due to compressing the bags loft. I think I will go with direct experience. I have since reduced the bulk of my old bulkey down jacket(500FP) with an 800FP down sweater, rated about the same temp. Now I sleep comfortably down to about 25F. Same layers on my legs and feet in general.

The EN ratings also allow for this. The maximum fill allowed is 800. But, allowing for the differing insulation effects of varieties of duck and goose, the insulation effect can be higher, *WITHOUT* changing the loft. Or, conversly, compressing the down can mean loss of loft with the same insulating effect. This is one of the reasons I much prefer the EN ratings. Somewhere, I was reading that Eider down will insulate to the *equivalent* of 900FP under this system, even though it only lofts to 800. Goose down varies, but generally insulates about 800 when it lofts to 800FP.
Anyway, lofting is the most important variable in retaining heat, but not the only variable. Else, we could simply use an air filled sleeping bag.

Heat conduction within a down fiber is important(the thickness and length of any barbules.) How much dead air it traps is important (the number of barbules and barbs.) As well as the angle at which the plumes interlock. The age of the bird the down was taken from. The condition of the bird. And so on…lots of variables, not simple loft, though this is easiest to sell.

Overfill? That is just a way of saying filling a bag that was improperly filled to begin with, or, for those that will be using their bag heavily on a three month trek. Down is forgiving. Once it has reached it's maximum loft, it is usual to add a half ounce to two ounces to make sure of any unevenness in batches. Cheap outfits will not do that. I suspect you could overfill a top quality bag by two or three times what they have and not see two or three times its performance. Down should not be loose in the chambers, nor be tight. Adding a bit may indeed help a little by trapping smaller pockets of air, yielding some small, as you say linear, increase in insulating value. This is not economic nor commercially feasable for most companies. the competition for light weight for best performance is just too great. This is where most companies stop their fill. So, Richards findings are likely accurate, but have little meaning to a commercial company. Though WM and others still offer overfilling as an option.

Like Dan was saying, older bags were less concerned with lofting since they were likely a poorer grade of feathers. Heavy fabrics, plastic liners inside canvas shells for example, were also typically heavy. They performed well enough to get people to the south pole! Newer stuff is better…and more fragile.

how exactly is it rated … can people really tell the difference?

the euro bums have what is generally considered a more stringent rating … who is to say that WM as indicated above isnt just being conservative

will you get 900 fill power in real world conditions?

i suspect its mostly marketing or definitions

WM bags are en-rated, FF are not … whether that matters is up to you

edit to add … i saw yr temp range … en-ratings to not apply at those temps …

En ratings apply to temps down to -25C/-13F.