650fp vs 800+

[Reid]

I'm convinced that my 650 fill bags retain warmth better than the 800 fill bags. I am guessing because there are more "clusters' of down in the 650's. Can anyone else say they've had this thought come to mind?

[Chatter]

No.


Seriously, though, this raises an initial question which is:
Could the difference be fewer feathers and larger down clusters for higher loft rating?

What other reasons are there for higher loft figures?

It stands to reason (and at least my experience) that higher loft ratings in quality gear is definitely warmer than similar gear with lower loft ratings (not to mention the lower total weight of down filling needed).

[tammons]

Basically trapped air is what keeps the heat in so I dont think it would matter.

The less air circulation inside the bag the better heat retention.

650 loft would have more down feathers per loft, so I guess with 850-900 down if it was barely filled to the same loft could have some clumped up thin spots and that could do it ??

Maybe construction techniques between the two ?? Letting some convection through on the colder one, or maybe its just over rated.

[Reid]

No.


Seriously, though, this raises an initial question which is:
Could the difference be fewer feathers and larger down clusters for higher loft rating?

What other reasons are there for higher loft figures?

It stands to reason (and at least my experience) that higher loft ratings in quality gear is definitely warmer than similar gear with lower loft ratings (not to mention the lower total weight of down filling needed).

Well loft is a relative thing too right? 5 inches of 650 could very well be more insulating that 5 inches of 800. I trust experience as you say you have. I'm still wary though.

[Mags]

http://en.wikipedia.org/wiki/Fill_power
http://www.comforthouse.com/refsafves.html

To sum it all up:

Fill power is a measure of the loft or "fluffiness" of a down product that is loosely related to the insulating value of the down. The higher the fill power the more insulating air pockets the down has and the better insulating ability

Generally speaking, any bag of 650+ is going to be reasonably accurate in rating. (My favorite budget bag is considered by some to be less accurate than stated. Others say no different. YMMV).

Generally, higher quality down bags (Feathered Friends, Western Mountaineering and others) use higher fill power down (which traps air better than less quality down) and tend to be a lighter bag.

Better quality down means less down needed to do the same function. That's why a 20F bag from one company with lesser quality down tends to be heavier from the other brands using higher quality down. (among other reasons)

"Some comforters with higher fill powers may have less down than a lower fill power comforter. This is to keep the comforter from becoming too warm."
(for a down comforter..but close enough. )


So..will a bag with higher fill power be warmer? Not necessarily..but many budget bags (and synthetics) have less accurate ratings than higher quality bags with higher fill power.

OR..to REALLY sum this all up "Ya get what ya pay for". Even a dirt bagger like me suggests buying the best bag you can afford.

[tammons]

Well loft is a relative thing too right? 5 inches of 650 could very well be more insulating that 5 inches of 800. I trust experience as you say you have. I'm still wary though.

Well I dont think so.
It all has to do with the exterior and interior material, construction type too etc.

IE a V baffle bag will be warmer than a box baffle bag IMO because it will hold the down in place better with less clumped thin spots and just by its nature you should not have any thin areas at all.

If both bags have the same loft, both have the same shells, both have the same baffles and consturction, and the down is evenly distributed with no underfilled baffles they should be the same.

Seems to me that the older bags were overfilled soemwhat. They definately used heavier shell material.

Todays bags with everybody trying to save the last gram, they are made with micro thin nylon and even though they have the advertised loft the down is at a bare minimum to make that loft. Very skimpy.

I would rather carry 2 oz extra and have an extra 1700 ci of fill.

[garlic08]

After owning one 650 bag and one 800 plus bag, I must disagree. In my experience, there is no comparison. But with only two bags to compare, I'm no expert at it.

[Marta]

I'm with Garlic here. 800 is amazing.

My take on the differences as you step up in grades (and cost) is that the lower/cheaper down has bigger and bigger spines on it. The highest grades of down are all fluff, no spines. One of the reasons down degrades over time is that repeated compression can damage it. Cheaper down gets much more badly damaged by compression because the spines of the feathers get broken and can't spring back into shape when the pressure is taken off. Good down just fluffs right back up. Cheaper down, with those stiff spines leading the way, pokes itself right through fabric and migrates on out. Spineless down doesn't work its way out as readily.

It's not entirely wrong to look at construction techniques, though, because cheaper bags will cut costs all the way around, including using designs which require less fabric and less labor, as well as cheaper grades of down.

[Hooch]

I went from a fairly cheap synthetic bag to 900fp down for both top and bottom insulation for my hammock. This stuff is divine! Warm all night long and I've taken it as low as 10 degrees with minimal supplementation.

[BlackRock]

Well loft is a relative thing too right? 5 inches of 650 could very well be more insulating that 5 inches of 800. I trust experience as you say you have. I'm still wary though.

I agree with Tammons on this. No, loft is not relative, it's an absolute measurement. I'll try to explain and answer below in my "way too long" post...

What is Loft?

Loft measures the volume that a single ounce of down can fill. You take an ounce of down, toss it into a container and measure how much of the container it fills. Theoretically 900 is the top of the range, so assuming you had 900fp down you could toss exactly one ounce into a 900 cubic inch container and fill it to the brim.

How to compare loft ratings.

You pick a volume to fill, 900 cubic inches, and fill it with 650 and 900 fill power down. You would need 1.4oz of 650fp down to fill your 900 cubic inch container and 1.0oz of 900fp. Same container and dimensions, same volume filled, but still only 650 and 900 for the respective loft ratings. The term "loft" is simply misused alot by manufacturers. But that's only the setup.

Which is warmer?

1 ounce of 900fp down or 1.4oz of 650 in the same container? To give it some dimension lets say it's a 4 inch thick baffle that's 15 inches square (15x15x4 = 900 cubic inches). The short answer is 1oz of 900fp.

But Why?

To answer that question you have to take a closer look at the actual down plumules. Tammons and Mags hit the nail on the head with trapped air. The tiny filaments found in fibers of the down trap air, that trapped air is what becomes the insulation layer. So the more air the down can trap the better it can insulate. Higher quality down has larger more dense plumules with more filaments. It's probably easier to see this difference so I took some pictures for everyone.

The plumule below is from my stock of 900fp down. What you are looking for in high quality down are large very dense plumes with lots of thick "hairs" or filaments on the down fibers.


Now compare it to this next plume, taken from my 800+ stock. Overall it contains good looking plumes but a higher percentage are smaller and look more like the plume below. Both fill powers contain overlapping ranges of plumes, just think higher fill power means more of the bigger denser plumes found.


You can obviously see that it's smaller and has fewer fibers of stringy down hairs. You can even see the difference between the actual filaments and how the top plume has thicker more full filaments. It simply won't trap as much or as big of air pockets as the top plume. It packs tighter and takes more of it to fill the same volume.

Now imagine that same baffle example.

You fill one with the 900fp plumes and the other with the lesser quality plumes. From the exterior you'd have identical looking baffles, if you weighed them one would be 1oz and the other 1.4oz but... If you could actually count the total number of filaments in each you'd actually find more filaments in the 900fp baffle. It would simply trap more air pockets and insulate better.

Now to toss in a few wrenches...

#1: Higher quality down only comes from mature geese. I.e. big dense plumes like the one shown above. The dividing line is generally 750fp (please note my terms "generally", "usually", "mostly", etc). Usually anything rated 750 and higher is handpicked from the geese while 750 and lower is eaten. So your higher quality down most likely comes from Canada or Europe whereas your immature lesser quality down comes from Asia (about 50% of the market).

#2: Feathers are made from Keratin which is what our own hair is made from. This Keratin strenghtens over time as it matures into a very strong thick plume. If you pick it too soon or get it from immature geese not only is it smaller and less dense but its also made up of more fragile fibers that will collapse over time causing the down to lose more loft sooner. So that 650fp bag is going to flatten out and get colder sooner than your 800fp bag.

#3: Really only seen with super high quality down (750-800+ vs 850-900) is something called clustering or cling. Fully formed clusters start to form "barbs" on each plume. Basically longer thicker filaments that you can see on the fiber above. What you start to see are individual plumes clinging to one another. Those "clumps" of down not only hold pockets of air in the filaments but the interlocking fibers create new larger pockets of trapped air yielding an even higher insulation rating.

Well... Thats about it for me, I'm spent I hope you find it interesting. I sure do. I didn't even get into the cleaning or conditioning of down, feather count, sustainability or the conditions geese may be raised in for their down.

Lot's to it, but I firmly believe along with Garlic08, Marta and Hooch who have all posted since I started writing this up that high quality down is worth it.

Enjoy,
Evan
www.blackrockgear.com

[Mags]

Or as I put it originally :

OR..to REALLY sum this all up "Ya get what ya pay for".



I like one sentence summaries as I am not the brightest bulb in the box.

[Reid]

Mags is such a helpful little fellow.

[Reid]

I think it may just be the case that the 650 bag I have is thicker and a bit more comfortable for me than the 800.

[Mags]

Mags is such a helpful little fellow.

http://www.whiteblaze.net/forum/show...ighlight=paved

The sense of humor is lacking in this one.

[tammons]

Other things can work into it too.

How the bag is shaped, IE a montbell hugger is going to be warmer than a regular wide bag, IE less air and air movement around you body.

If it has a collar or if not and or how it is shaped around the neck and shoulder area, again a plus for the hugger without a collar vs a normal/wide bag without a collar.

If you move around a lot then you can pump cold air into a bag. That happens less with a collar or a more form fitting bag.

Also the hood is important. You probably lose more heat out of the back of your neck area than any place else. If you are a back sleeper and never move, and close down t he hood, no big deal. If you are a flip flopper or a side sleeper, then you will probably lose more around your neck.

Then there is the entire ground insulation issue, IE an Exped down or syn mat will make a bag feel a whole lot warmer. Those are toasty mats for sure.

[Franco]

The short answear to me is that all other things been equal , 800 is better than 600.

As usual a badly designed (or wrongly speceifyed ) product will still be so even if you use the best materials.
So if I made a sleeping bag with 500 fill or 900 fill I would still end up with a piece of crap except that one would be lighter.
Franco

[Rocketman]

There is some interesting work from the military on thermal insulations and density (which is not quite the same as "loft").

One of the reports or papers is below.

http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=ADA481751

Phil Gibson of U.S. Army Soldier Systems Center, Natick, Massachusetts is one of the authors. The figures are interesting to look at and to attempt to seek answers on heat loss in practical sleeping bags.

There is a masters thesis on something like "the mechanics of down", but that isn't the correct title. It too has a discussion on loft and feather content as well as some discussion of the nature of down.

http://etd.gatech.edu/theses/availab...00412_mast.pdf

Found it. You will probably find the computer modeling part less easy to read than the introductory materials.

I sent a copy of it to "Mr. Wiggy" of Wiggy sleeping bags telling him that there ought to be an equivalent paper on fibrous thermal insulations. He replied with his usual diatribe against down and worthless complicated mathematics.

There seems to be not much in the way of a giant amount of public data on the subject of the thermal and mechanical behavior of down.

So, lots of discussions end up with "in my experience".....

That has been my experience.

[Rocketman]

There is a fellow, Richard Nisley, who is a consultant on thermally insulated outdoor gear who writes occasional articles on www.backpackinglight.com.

Some of his articles are quite good. Others are.... well hard to understand.

As a consultant, there are probably limitations on what he can say, such as revealing much in the way of proprietary data that he gets from his customers.

There probably is a great deal more data and information on thermal insulations than you will find published in the literature or on the web.

So, we end up back where we were. Lots of talk, and slow progress in general understanding.

[Reid]

How much down can they actually get off one bird? Am I carrying around 5 or 6 birds worth of feathers while they are out there freezing somewhere?

[Reid]

There is some interesting work from the military on thermal insulations and density (which is not quite the same as "loft").

One of the reports or papers is below.

http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=ADA481751

Phil Gibson of U.S. Army Soldier Systems Center, Natick, Massachusetts is one of the authors. The figures are interesting to look at and to attempt to seek answers on heat loss in practical sleeping bags.

There is a masters thesis on something like "the mechanics of down", but that isn't the correct title. It too has a discussion on loft and feather content as well as some discussion of the nature of down.

http://etd.gatech.edu/theses/availab...00412_mast.pdf

Found it. You will probably find the computer modeling part less easy to read than the introductory materials.

I sent a copy of it to "Mr. Wiggy" of Wiggy sleeping bags telling him that there ought to be an equivalent paper on fibrous thermal insulations. He replied with his usual diatribe against down and worthless complicated mathematics.

There seems to be not much in the way of a giant amount of public data on the subject of the thermal and mechanical behavior of down.

So, lots of discussions end up with "in my experience".....

That has been my experience.

Nice.
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