Difference in warmth of 800 vs 900FP down FOR THE SAME BAG

Ha, ha…you probably couldn't tell in a bag.

900fp is is a magic lab number you never see in a real bag. And it would compress slightly more and a bit faster, even if you could get it. It is all advertisement above 800. Even the best of the Eider downs only ever loft to ~800. They just create finer pockets of trapped air…isolated, ultra fine air pockets does most of the insulation job. It is fairly water proof, but like a plastic film that is shredded, it can still pick up and hold large ammounts of water. So, treat it as non-waterproof.

Won't be any warmer if constricted to existing baffles, just slightly lighter.

@chris – well obviously i could put in LESS 900FP and get the same loft. the diff in weight would be roughly 10% as the diff in loft is about that (same principle as 650vs 800 really). but i was referring to putting in the same amount in Oz

@james – assuming the same guy/lab does the testing to reasonable repeatability then the test is the test….so lets assume the numbers are comparatively correct. so one could assume that the finer down will create finer air pockets etc…why is this so different than 650 vs 750 FP

This has been discussed before and the science covered by Richard in many other threads. Down can be compressed up to 2.5x and still maintain the majority of the added warmth. If inches of loft is the end all, then minimizing the down in the baffle while barely filling the chamber is where you should go. A number of companies do this and owners of these bags complain.

All things being equal, and if the fill power is accurate, then two bags, one containing 800 fill and another containing the same amount of 900 fill down, would vary in warmth with the 900 bag warmer. The question is how much warmer and is the added cost worth it?

>Won't be any warmer if constricted to existing baffles, just slightly lighter.

Not necessarily. There's a certain amount that you can compress down where it doesn't lose warmth. If I recall correctly from another thread, I think it's something like up to 2.5x compression of the original loft will retain the same warmth. So, by over stuffing, you could theoretically get a warmer bag with the higher fill power down–up to a point…I think… :). The scientists will know more.

But, the loft debate still goes on.

Edit: John beat me to it while I was typing this post.

i remember some threads by Richard… but going back to them recently i cant find the direct equations that include both fill weight and FP so i can extrapolate the relative warmth.

Re cost – since custom high end gear is $$ if i knew the warmth added was 10% and needed to shell out and extra 5USD per ounce for the difference i would prob do it – adds up to 50-70bucks for my normal warmth bags

EDIT: also all those threads were about different densities of 800FP down and not same density of different FP down

"This has been discussed before and the science covered by Richard in many other threads. Down can be compressed up to 2.5x and still maintain the majority of the added warmth. If inches of loft is the end all, then minimizing the down in the baffle while barely filling the chamber is where you should go. A number of companies do this and owners of these bags complain.

All things being equal, and if the fill power is accurate, then two bags, one containing 800 fill and another containing the same amount of 900 fill down, would vary in warmth with the 900 bag warmer. "

+2

Within reason, down can be compressed without losing significant insulation value. So using 900fp down would overstuff the bag by 12.5% (900/800) and give you about that much more insulation. It's slightly less efficient to have the down compressed, so the 900 fp down might end up having 11% more insulating value.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=39920

Ryan Jordan
( ryan – BPL STAFF – M)

The kicker is that we ran the same test next to down taken from a manufacturer's 750 fp bag. at 50% humidity, the fp was 720. Why? It had more feathers that were stiff enough to preserve the loft in moist conditions.

OMG – so many parameters – dunno what to do. the 50% humidity is interesting…though the argument from the luxurylight guy was not about humidity but the time it takes to loft.

Still – it seems that everyone is going for hi FP down (be it 750/800 or 870/900) – so are people feeling COLDER in their new bags???

Assuming i have a choice (custom bag) and the $$ aint so bad – how do i work the optimum here?

michael …

i believe the point in the above post is that some of the "900 fill" down is basically a figment of a marketing hacks imagination in real world conditions …

900 fill here could mean 800 fill in euroland …or something else at some other company …

the euros generally have more conservative down ratings …

just buy what you want and dont worry about it too much …

I well understand that feeling.
I have been looking around at stuff for the past couple days. (There isn't a lot to do around here on cold winter days…) and it seems that the various testing is likely about the best summary you will find.

800+FP down is lighter and warmer if it is fairly dry, but degrades guicker if damp or wet than 700fp down. I will not dispute these findings, indeed, they are far more rigorous that I have ever done. I suspect that loss of loft vs fill weight does cause some loss of insulating value, but this is not linear as you would expect from other poasts on overall performance of insulation. Compression of any air pockets inside the down would lead to increased efficiency of the insulating value (by creating smaller air pockekets, perhaps more of them due to the fibers rolling) without greatly increasing the conductance of heat by the denser materials making up the fill. So, some compression would likely be OK, with only a slight loss of thermal insulation. Anyway, just a guess…

Soo, that leaves the conditions of "where" you do most of your hiking. If in the northern parts of the US, a mix of rain and dry weather, perhaps a 700FP bag might be a better choice, based on weight (good weight), excelent insulation, good dampness resistance, and fair cost.

An 800+fp down under the same conditions will have excelent weight, excelent insulation, poor dampness resistance, poor cost. But, 800+fp would be a better choice for dryer conditions, generally.