Goose Down Question

I was considering harvesting the down from an older sleeping bag for a new project, but since it's probably 600 fill power rather than the 800+ that's available today, I've been trying to decide whether it's worth it, weight-wise.

So, this made me start re-thinking about down. Down works by stabilizing air. Air is a poor conductor of heat as long as it can't move around (convection). So, that means that the down that stabilizes the air best provides the best insulation.

Now, if you had some imaginary 10,000 fill power down, it would be very light, but the air spaces would be relatively large, and the air wouldn't be stabilized that well. If, on the other hand you had some, say, 50 fill power down, it would be heavy and very dense, and there wouldn't be much air in it to stabilize.

So there's a "sweet spot" somewhere in between. Is it possible that 600fp down is actually slightly better insulation than 800+fp down? Obviously, the higher fill power results in a lighter sleeping bag (or coat or whatever), but how does 2" of 600fp compare to 2" of 800+fp?

I have noticed that some of my older down articles seem warmer, but there are construction differences that make direct comparison difficult. For instance, I have an old Camp7 duck down jacket with 65/35 cloth for the external fabric that's warmer (it seems, anyway) than my Montbell Alpine Light jacket, which is puffier and has "better" down.

It may be that I have too much leisure time Anyway, I'd be interested in your thoughts.

My not very scientific thought is that you're absolutely correct about there being a sweet spot but that we probably haven't reached it yet, even with the higher FP down. Think about the reflective insulation in a Neoair pad for example (not down I know, but stay with me). The tubes in them don't extend the entire thickness of the pad; they're smaller and stacked. The idea I believe, is to allow for less convective heat loss, but even so, the air space in these tubes/channels is orders of magnitude larger than the air spaces in high FP down, and yet a Neoair pad is still plenty warm. That's why I think we haven't reached the sweet spot yet with down.

I've wondered for a long time whether some combination of clothing-style Tyvek and long, skinny balloons (like the kind used to twist into balloon animals) could be used as a compact, light quilt. How skinny would the tubes have to be to reduce convection sufficiently for use as a top quilt? Maybe by the time the balloons got skinny enough their weight would exceed that of down. A sleeping pad has to support weight so the situation is a bit different. Still, I wonder if there's a use-case for a tiny, light one-time-use inflatable insulation system. Maybe a trail runner who's worried about an unplanned bivouac and is as concerned with volume as he is with weight could use balloons to augment a SOL bivy sack.

That balloon rubber is pretty heavy. Sealed aluminized PE (i.e. Mylar or Space Blankets) tubes would probably work better, and they would have the advantage of reflecting radiant heat inward as well. The trick is figuring out how to seal it effectively. I've never tested with emergency blankets (soon), but I bet they require some type of adhesive vs heat sealing, because of the metal coating.

SOL (IIRC) actually demoed an inflatable 2 or 3 years ago that fit exactly the purpose your talking about, a one-time-use inflatable. It seems to have disappeared without ever going to market. Too much liability maybe? IDK.

I know people heat-seal mylar food bags for long term food storage all the time, so seems like heat sealing vs adhesive would work just fine.

If you’re using a number of separate balloons, the trick is “How do I inflate it?” You can’t seal the air inside, for obvious reasons, and if I recall, those balloons take a lot of force to expand (and I have the red face to prove it, at several preschool birthday parties for my kids.) Yes, I know they’re not going to use exactly those balloons for what you’re thinking, but you’d still have to overcome the initial inflation resistance. So, would the balloons have to somehow be interconnected to allow inflation?

I know foam clothing and sleeping bags were commercially available for a while (even getting mentioned in one edition of Chris Townsend’s Backpacker’s Handbook), but it’s been years since I’ve heard anything more about them. Guess they didn’t work out, either?

Simple, an utralight helium canister. It gets lighter the more you put in.

Sorry, OP, for taking an interesting question so far off the rails.

I find this question(s) interesting because I have researched that subject online and thought about it, and have quite a bit of experience with down garments. I know what you mean by saying that older garments "feel" warmer. Perhaps it is just the weight. Also, my ultralight down jacket doesn't seem windproof. Nevertheless, my new 2 pound NF (850 fill power) sleeping bag seems about as warm as my old REI McKinley (near double the weight, probably 600 FP). But the shell of the new bag is Pretex and the design of the quilting and the distribution of the down may be better. I found lots of seemingly scientific information on Backpackinglight.com regarding the design and arrangement of various down articles. My conclusion was that every item needs to be tested individually because there are way too many variables to make assumptions based only on simple things like fill power.

The "sweet spot" may be a range. But is it 600 to 700 FP, or is it 700 to 850? Is it narrower or wider? All difficult things to ascertain without a lot of assumptions and experimental evidence. My conclusion, after some research, was that I could survive almost all
expected conditions in a well designed bag that weighed a Kilo or less and had down FP of at least 750. If you look at the European standardized temperature ratings and fill power and weight i think you will see that the higher FP bags of similar weight have better (lower) Temp. ratings. That correlation says something.

Recycling the down seems like a good idea. However, I made an emergency (bivouac) elephant's foot bag from an older down garment and the result weighed more than my lightest summerweight bag and I am quite certain that i would be better off taking the summerweight bag than my DIY elephant's foot. Hmmm....

Still interesting. let us know what you decide.

I'm replying once more....because I did a little looking around and comparing fill powers in sleeping bags and temperature ratings. Within the practical ranges of fill power there seems to be a direct correlation between warmth and fill power, all other things equal. More density does not necessarily equal more insulation power (think of heavy synthetic insulation as an example). I looked at seven sleeping bags of comparable design and the same rating and I found that in fact in every case higher fill power resulted in a lower temperature rating. (spreadsheet available on request).
Like you, I had thought perhaps my old low fill power jacket was warmer. It might have been, but it could have been just as warm and weighed a lot less if it had higher fill power down. I don't think there is any getting around that.

"Seemingly scientific" is right. Still, higher fill power generally equates to more loft (for a given weight), which is what determines warmth, other things being equal, which they usually aren't.

Interesting that Western Mountaineering is the only manufacturer honest enough to state the loft of their bags.

The higher fill power down is usually combined with the lightest shell fabrics, which probably accounts for some of the feeling that "older is warmer."

My "project" is just in my imagination at this point. I'd like to try a quilt, but have doubts about whether it would be right for me, as I get cold easily, and I can't justify spending a lot of money to find out. So, it occurred to me that I have some high quality down available, just lower fill power than the current 800+. But would I end up with a 2-pound quilt? Guess I'd have to do the math...figure the dimensions, volume, etc., to get an idea.

You said you get cold easily. That is another one of those variables that is almost impossible to account for. I am the opposite. When I am out with my friends I often hike with it is not uncommon for them to complain that they were cold when the temps have gone below freezing at night. One has a "Feathered Friends" with even additional down added so his bag's rating is lower than mine, yet he gets colder. (He is also taller and thinner than me and I think my fat helps keep me warm.) Another friend uses a rather nice bag PLUS an ultra light quilt, probably with 800 FP down. He also complains of cold when I don't.
I am very pleased with my 3 season bag, but then I am a warm sleeper apparently. It is a NorthFace hitail 3 season. I simply add long-johns and a bivvy cover for winter.
https://www.trailspace.com/gear/the-north-face/hightail/

I meant to say that I looked at a number of sleeping bags of the same design and temperature rating and in every case those with a higher fill power rating weighed less. In other words a pound of down with higher fill power insulates better. So the old jacket with 650 fill power might feel warm, but it seems that a jacket (all other things equal) with higher fill power would be lighter if it were just as warm.

Someone once said that the ability to insulate is about proportional to the thickness in a given material. Fill power = loft per ounce. So more fill power = more loft = more thickness per ounce = more insulation. Make sense?

Yes, that makes sense, and I think it's correct. I've just never seen any discussion of the density of the fill material. That is, whether some fill material is more efficient than others. It's sometimes said that it wouldn't make any difference, as far as insulating ability goes, if the fill were goose down, steel wool, or shredded newspaper, if the thickness was the same. It would seem there must be some difference, as some fill materials would hold the air "deader" than others.

So, I was wondering if lower fill power down might be slightly more efficient than higher fill power down, since it's probably a bit more dense and therefore might hold the air more still. I'm guessing that even if that were the case, the difference would be close to zero.

For those who follow such things on "the other lightweight backpacking site" (BPL, the one you have to pay for), there are technical articles and, especially, posts by Richard Nisley, who has access to lots of very technical materials testing equipment. Anyway, they confirm that down with higher fill power definitely has less weight and (when compressed) bulk for the same amount of warmth as the low fill power. The higher fill power down does require more fluffing up after being compressed in the pack, though! And with the price of down heading for the stratosphere, is the higher price really worth the relatively small decrease in weight and bulk?

BTW, I quit BPL several years ago in protest against their policies, but occasionally (every few months) browse their forum for posts of interest. There aren't many for me any more, since I have no desire to acquire new gear and since old age is definitely slowing me way, way down.

I just came upon this article, which points out how we've become enamored of buzzwords like "fill power" and other examples of what the article calls "technobabble":
Industry Terms , Outdoor Gear, and Marketing Buza

The conclusion is to get what suits you best! In the meantime, it's a very interesting (and amusing) read, which certainly reminded me not to get carried away with this stuff!