Down filler bags – full body, or half-body pied d’éléphant?

Or…get a mummy bag…

Re: PHd not having customer reviews. I used to work in a bookstore–well, a small chain of three bookstores. When yelp came along, we’d get completely off the wall reviews from well known customers with some weird-ass gripe. and they had it in for us.

Not everyone is an informed, experienced, rational reviewer. Yelp isn’t Plato’s Symposium. A lot of false information can be conveyed in customer reviews. PHD may have simply decided it wasn’t worth it. I understand.

I’ve learned to read customer reviews of products with a good amount of scepticism going in. they can be helpful; most often are! For sweaters and shirts. For technical gear? I wonder.

Agreed! PHD are regularly reviewed by knowledgeable and trusted reviewers like Chris Townsend – much more reliable. Apart from that they’ve never done much marketing that I’ve ever noticed. Like most small artisan gear makers they mainly rely on word of mouth from happy customers. They’ve been there for many years so they must be doing something right, even if I can’t personally afford their kit.

As for sites that do display reviews – how far can they be trusted? I once wrote a respectful and considered 5 star review for a well known cottage manufacturer, outlining all the reasons I loved the product. But then I added a section explaining that as with any specialised ultralight product there are also trade-offs to take into account, and outlined the downsides.

The review is still there – minus the list of downsides…

But back to filler bags – actually the product is explicitly designed for mummy bags. Even with a relatively tight cut such as my Rab there is still a fair bit of dead space – otherwise you couldn’t get in and out of the thing, or move about.

The idea of the filler bag is to eliminate that dead space, but with a compressible lofting medium like down that still allows unrestricted movement.

that’s funny, they removed the list of downsides???

but that is useful information.  They shouldn’t want someone to buy their product, then be disappointed because it’s not robust enough and return it, write a bad review…

YouTube certainly isn’t a scientific journal. Like Wikipedia, you can’t put much faith in the reviews. They serve as a starting point. Using a few smarts, l think most folks can distinguish the difference. There seems to be a lot on Reddit. Mostly just a few grips about a loose thread here and there. Fill power and weights. Not much about filler bags. I meant no offense. The only person I’ve ever known that was from Yorkshire was Lord Hanson. Maybe his staff. Maybe Lord White  in passing.

The whole time I’ve been reading this thread, one thought keeps crossing my mind: the whole point of a mummy bag is to fit snugly and eliminate dead space. The only use case I can legitimately see for a “filler bag” is if you have a mummy bag that doesn’t fit properly. Of course, maybe that is a common scenario, since many people might prefer a loose-fitting bag for warmer conditions, and then might want to add something when it’s colder.

But a universal claim that you can increase the temperature rating of a properly fitting mummy bag simply by ramming another bag inside it … that just doesn’t make a lot of sense to me.

https://rockfront.eu/product/all-season-system-ul/

good point Dan, we’ve solved this problem, with a mummy bag

the bag is next to us all the way around, no gap

Huh? We’ve solved this problem with a mummy bag?

George H’s post earlier in the thread addressed that question.

It will be very constricting, to the point of being unusable to size the outer, main bag for a fit close enough to eliminate the majority of dead air space. This is simply not an option, imo.

Which leaves the filler bag, or deal with the air.

https://backpackinglight.com/forums/topic/down-filler-bags-full-body-or-half-body-pied-delephant/page/2/#post-3823050

Slight revision: the problem with the air space inside a mummy bag is precisely that it isn’t dead air space. If it were truly dead, like the spaces between glass in insulated glazing, there would be no reason for a filler, since it would be acting as insulation. The problem is that the air space inside a mummy bag needs to be heated, too, creating an additional drain on warmth.

good point, problem no longer solved : )

then if you put in a down filler bag it will be very constricting, to the point of being unusable?

I think there’s good info here for people.  Different people have different tolerance for being too constricting

One of the reasons people like Ryan started using a quilt was because of the advantages of “variable girth” for layering, which a mummy design doesn’t have. Variable girth was one of the original selling points for the first Arc X made by Nunatak to Ryan’s/BPL’s specs.

But when temps drop well below freezing, the utility of quilts becomes questionable. Looks like Ryan himself now favors a bag.

I have one of the original Arc Zero quilts made by Tom Halpin when he first started Nunatak. Puffy and light (and beautiful in that original blue UL sleeping bag fabric from Dimension Polyant paired with contrasting Pumpkin 40D Epic at the foot and head along with a 30D silnylon strip inside the head) though it may be, it isn’t as warm as the fully enclosed 10 degree Sastrugi that Nunatak under Jan made.

I use both of those with overbags in very cold or very wet weather, but the function of overbags is totally different from the function of a hypothetical filler bag.

I’m willing to bet that if I put a properly designed filler inside of my Timmermade Serpentes 20F bag (432 grams!) that it would be just as warm as the plump and beautiful 10F Sastrugi for about 200 grams less weight. And if I put it inside the Sastrugi, that would be warm well below 0F (with proper head covering).

then if you put in a down filler bag it will be very constricting, to the point of being unusable?

I agree. That’s why I suggested earlier in the thread making it a bottomless and strapless narrow quilt design with a closed footbox to keep it in place.

You’d still need a larger bag, which might be fine for your needs. An over quilt has the ability to expand. A mummy bag doesn’t. If the fastener points are further up on the quilt, it will drape around you.  I think in Jerry’s depiction, the quilt wasn’t wide enough to drape down. Mostly it’s a draft problem.
https://rockfront.eu/product/600-ascetic-ul/

https://zenbivy.com/pages/light-bed-minus-5?srsltid=AfmBOorozH_wkatVFnhCxEbP3s3IMPsDdGKMx7sbyZGZ2oxiPQiDzlq0

if the quilt edges go down to the sides of the pad, and under with straps, then you can get an open area on both sides towards the bottom

That’s what happens to me

My blanket at home has the same problem.  It’s much wider than me so the way it drapes it creates an open area.

I can sort of tuck it under me and that takes away the open area.  But when I roll around the open area returns – I can’t roll when I’m sleeping such that it stays tucked under me

I think the key to staying tucked in is raising the connection points on the quilt.

My blanket at home has the same problem, too. What a coincidence (not!). That’s why I use a very light 7D down quilt inside layers of wool blankets at home. The down quilt naturally fills in the spaces inside the blanket.

We’d probably need a different thread to discuss the Zenbivy system that Terran linked to above. I’d have a number of questions about the design. It looks easy to expand the girth and avoid drafts but not as easy to then constrict it back again, especially not throughout the length of the bag — especially not given the semi-rectangular design. It looks to me like you will inevitably end up with extra air space inside. The combo of the -5 light quilt and -5 light sheet is significantly heavier than my Sastrugi with a hypothetical down filler would be. For about the same weight I could still add an overbag made with Alpha 90 and Argon .49 7D, giving me greater warmth (I think it would be much warmer) and far superior moisture management.

That’s right. A down quilt will do that better than a wool blanket. If the bottom is curled in, that becomes your filler.

Insulated over bag.

Options

UL Overbag + Apex Insulation (with compression sack) + mosquito mesh
UL Overbag + mosquito mesh
Apex Insulation (with compression sack)

I primarily use a quilt system, even to -5*F.  When it gets near those temps, I’ve experimented with using an IR reflecting VBL and found it can be helpful. On one hand, you can’t wear clothes puffy insulation within the IR reflecting VBL, which is kind of a negative, but on the other hand if your quilt/system is warm enough you might not need to.

Unfortunately another issue specifically with IR reflecting VBL’s is that it will only reflect IR where there is a free air space between you and the surface of the VBL. That means the part of the very top of you will not be reflecting IR most likely (since it is being pushed down by the weight of your quilt or bag), but in those gaps on the side, it could. Also, if it is not cold and dry enough, it can increase humidity enough to cause condensation, which will reduce the IR reflection. (This is why you get much less sky window IR radiative cooling with cloud cover vs clear, dry skies).

Anyways, some of them are quite light weight and cheap, maybe worth experimenting with? And IR reflecting or not aside, VBL’s have the nice benefit of keeping most of the extra moisture out of your sleep system. You do need a good baselayer system that handles moisture well though.

But I’m more in the camp of wearing insulated clothes inside the sleep system, all in all. But if that is not acceptable, I wonder about taking a large piece of fabric, getting a very light weight synthetic insulation and attaching a little insulation to the sides of that fabric to fill in those more void air spaces on the side.  Could be made very easily and cheaply.  It would only weigh an ounce or two more than the product that uses very expensive down since most of it would be a single layer of fabric without insulation (and with no sewn through baffles).  I’m just not sure if it would stay in place well or not. Probably depends on the type of sleeper you are.

If we slept in the same position and had body mapped insulation that was fluid as air. Given proper insulation, the air gap should be warm air anyway. This is a solution to a problem that doesn’t exist. Complicating simplicity.

“the air gap should be warm air anyway”

that is a good theory.  I think it’s correct.  I will measure the temperature sometime when I’m sleeping to verify

Heat is energy. Cold is nothing, the absence of energy. Hot will flow to cold.  Your body will warm up the air and will warm up anything in the bag. If there is a barrier, you have resistance. Like your car battery. Power will flow until it’s equalized. Unless there’s resistance. Air is resistance. A very smart electrician told me once, “it’s all fire”. It’s all about the flow of energy. At least that’s my simpleton explanation.  Make sure you eat. That is the fuel for the fire.

I’m open to correction.

If you have 2 insulations in parallel:

DT1/R1 = DT2/R2

R1 is the insulation I’m wearing, R2 is the quilt, let’s say they are equal just to make things less complicated

Then DT1 = DT2.  T2 is half way between outside temp T3 and skin temp T1.

If significant cold air was leaking into the space, or there was convection or whatever, then T2 will be significantly less than halfway between T3 and T1.

If I measured the temperature of the airspace and it’s about halfway between outside temp and skin temp, then we aren’t leaking heat – no need for a filler bag.  Or, no need to figure out how to get your quilt to better drape down and stay against your body better.

That’s my theory : )

I’m already in over my head.
If T1 was 100*, T3 was 0*, and R1 was a single layer with an accurate comfort rating of 0*. Hypothetically, there is no heat loss. Now add a second layer, R2. Is T2 50* or 0*?