Why waste money, weight, and space on down...or ANY fill for and UQ?

[C_Claycomb]

Kudos for the hand sew! I once made up a 4m x 3m pertex tarp with a hand crank Singer and reckon that must be easy compared to what you are doing!!!

Oritron covered all the stuff I was thinking about insulation misconceptions.

I have my doubts doubts about fabric baffles as an UQ. Here are the things that trouble me, or that I think could be problems:

• To adequately prevent convective heat transfer and a cold butt one might need so many baffles that the effort and complexity of execution outweighs the small weight benefit.
• When I looked at R values, there was an inverse relationship between the size and open-ness of air pockets and the material's effectiveness as an insulator. Closed cell was better than open cell and open cell was better than down. Large open voids significantly bigger than the air pockets in down don't seem likely to be warm.
• If you make enough baffles you lose your weight advantage.
• Biggest problem I see is maintaining the gap between layers without any filling keeping them apart. Baffles will collapse if the wind blows against the UQ. If the outer layer of fabric is the same size as the inner layer the baffles will get collapsed through a combination of the weight of the inner layer, and tension in the outer.

All those Thermarest type mats are inflated, and it is the air pressure that keeps the space open. With nothing creating pressure between inner and outer layers keeping the insulation gap will be difficult.

Might be onto something if you use half the down and alternate between down filled and empty channels, that might help with the structure and gap.

Can you make up a scale model to test the ideas?

[Helium33]

I have been hand sewing my down TQ, I'll try to get some pics up when she's finished. Since it is being hand sewn, I have had lots of time to meditate on the design for my UQ...which i will also be hand sewing...after I finish the winter tarp. During my meditations I realized that the down in an UQ doesn't really do all that much to improve the efficiency of an UQ. On a TQ it is pushing the 2 layers of fabric apart to maintain the 1-3 inches of trapped airspace, and the trapped air is what is keeping us warm. But, on an UQ we have gravity working for us. In theory, with slight modifications, one could easily make an UQ shell that hangs with a relatively uniform space between the 2 layers of fabric and works just as a down filled one. The only real catch is that the shoulder area might need some help staying at optimal fluff.

My idea was to have the two layers of argon 90 with a 2 inch strip of webbing sewn between them around the perimeter (similar to the way baffles are generally sewn across the middle). Argon might work as the 2 inch strip, but I figure the stiffness will help it keep the 2 layers apart in the corners. Also, I would add a baffle (of any material) down the center (lengthwise) to keep the bottom layer from sagging too much. Everything else would be pretty standard, cinch cords on the head and foot, shock cord along the length for suspension, etc. I have also played around with the idea of having the top bit of fabric a few inches narrower than the lower fabric. The idea is that it would be easier to sew than darts, and should minimize compression (this is something I will mock-up once the rest of my fabric arrives).

For those that have months and years of UQ R&D experience under their belt, I challenge you to give me one good reason why I should put down in my UQ....other than the fact that I'll have 7 oz of the stuff left after I stuff my TQ. Thanks for the feed back.

I get the theory. It seems like it would take a lot of fabric to achieve results.

[CamoDeafie82]

I went the cheap route and used a shaped open cell foam pad underneath my hammock for a couple hangs; as bulky as it was, it was rather light, and it was only 2" of foam with the gaps and such...it worked OK down to the 50s, but below that, it wasn't good. I had only one layer of DWR ripstop fabric for the shell, and it was essentially a garlington taco of sorts.....
The idea was that the air pockets and the open-cell construction would give me a similar insulation method as UQs, but it didn't work out as good the last time I used it, because it was falling apart. Granted it was from a cut apart Wal Mart open cell bed topper.
SO I went straight for down UQ made of the two Costco Down throws; and it insulates much better than the open cell foam and the modified synthetic sleeping bag UQ.

[oritron]

So, I want to understand what you're proposing. You want to nix a down and baffle design that involves 9 straight sewn baffles for an intricate pattern of noseeum mesh triangles that are 3/4" on a side? I would dread having to do that sewing.

I'm saying that the fabric by mass equivalent lets you do very dense triangles for the same 1yd^2 × 2" volume. I'm not saying "make this design instead", just that you have a lot of material to work with in trying possible baffle designs… obviously less dense triangles would use less fabric and be less work to make.

If you use 6 sq yards or less of 0.5oz fabric for every 1 sq yd area of underquilt, you're already saving weight compared to 800FP down at 2" loft—and that's not accounting for overstuff.

Basically, you're getting down to the same thing that the down itself is doing: trapping smaller amounts of air in a space so there is less air movement and heat transference.

Absolutely, that's the idea of any underquilt. The question is, can you do it better than the current approach? 'Better' could be an improvement of packed volume, weight, or cost.

BA's website lists non insulated air core r value as 1.5 and the insulated ones start at 4.5 or so. Again adding something like down to get better results.

The NeoAir All Season pad only uses triangular baffles (no down, no synthetic insulation) and manages an R value of 4.9 for an all-weather pad with a 2.5" thickness.

oritron... Double and triple pane windows are filled with Argon gas, not air.

Thanks Goobie, you're right. Mostly argon but occasionally other noble gasses are used as well. The idea of an optimal gap that doesn't support a convection cell is still the same though, which holds as long as the fluid in the gap has a density which varies with temperature.

To adequately prevent convective heat transfer and a cold butt one might need so many baffles that the effort and complexity of execution outweighs the small weight benefit.
…
Can you make up a scale model to test the ideas?

IMO that's really the main question here Claycomb, and put succinctly too. Can a baffle-only design provide any improvements? Maybe, maybe not. It warrants some further examination.

[WalksIn2Trees]

I concur, reflective space blankets, reflectix, reflect radiated IR back at the source, and no it doesn't breathe, although there's a space blanky that claims to be breathable, but I haven't tried it. Reflectix also acts as a minor insulator, and if multiple layers are used it's insulative value can be extended.

However, down is far and away much better. You can't argue with evolution, bazillions of generations of ducks and geese can't be wrong

[Hobopelican]

However, down is far and away much better. You can't argue with evolution, bazillions of generations of ducks and geese can't be wrong

Don't forget that evolution is ongoing! Watch for the next mutation!

[Smithhammer]

You must live somewhere very mild. Enjoy!

I, on the other hand, don't live in such a mild place, and have had cold, sleepless nights even in June in a hammock. I now love my Phoenix UQ...

[Pyrogen]

Personally, I don't find insulation filling to be a waste of money, weight, or space. Trapping radiated body heat within pockets of air via natural or synthetic materials is an age old concept proven for centuries. I'm all for you being the guinea pig though, I hope your efforts pay off! Please document and share your progress with us!

[Trees company]

Not the best Idea... BUT !!! keep your invented mind going.. Always good to do things with your own hands .. Have fun with this Hammock stuff.. Good day , Jeff P.S Don't let the "NEG" stop your passion ...

right on some people here can be alittle harsh don't let it get you down H.Y.O.H

[Slugger]

The NeoAir All Season pad only uses triangular baffles (no down, no synthetic insulation) and manages an R value of 4.9 for an all-weather pad with a 2.5" thickness.

Not the same. The NeoAir has multiple reflective layers embedded into the design hence it's higher R value.