Downproof Fabric

I have used the 0.8 oz ripstop from Trhuhiker on a couple of down quilts with great results. I don't know what is going on with your Hydrogen, but in my experience it could be a couple of things.

My first impression, from what you said is that the down is not as good as it should be for the fabric being used. You said,"Everytime the bag is removed from its stuff sack, as well as every morning, there are a couple more feathers poking out through the fabric or else stuck to my thermals." Feathers ain't down.

The better down has very few quills or feathers. Technically speaking, down itself has no quills at all, but a few sneak into the mix. Higher rated down has fewer quills than lower rated down.

So-called down-proof fabric is actually quill-proof fabric. The term originated in the bad-old-days when separating down from the quill-bearing plumes and feathers was done by hand, and the best down had a fill rating of maybe 650 cubic inches. Today, high-quality down has few quills and does not need down-proof fabric, so you can use very light fabric.

There is a limit, however, because no down mix is without quills. The second possibility is that the particular fabric you refer to has an excessively loose weave. However, I find that unlikely.

The third possibility is that the manufacturer used oversized needles what left large stitch holes or that there is some other manufacturing glitch such as excessive stitch length leaving down channels inadequately sealed. Your reference to feathers tends to rule that idea out. But down can creep through small openings. What you get then is a wad of errant down – not feathers.

Paul,

As Vick stated, down and feathers are two different things. Down has no hard quill. But I wouldn't worry about this at all. Unless you've tried to stuff something with high fill-power down (like in your Hydrogen bag), or had a down item burst, you have no idea how much down is in there! You could lose as much down as you state losing for many many years, with no appreciable loss of loft to you bag.

As for replacing then down clusters or feathers that poke through, grasp the fabric on the opposite side of the bag as the extruding down cluster (e.g. if the cluster is poking through the outer shell, grasp it from inside the bag) and pinch your fingers around it, then pull it back into the bag. That's much easier than trying to poke it through from the outside.

Vic and Russell:

Thank-you very much for your insights here. I've cleary been thinking about this 180 in the wrong direction. To be fair, I actually own (2) of the bags, swapping a couple of years ago thinking the first was faulty. Never-the-less, my first one has served well for over (5) years being the go to bag 95%+ of the time. My rants are as much to do with B.S. marking on the part of Marmot as anything (900 fill my ass).

Ay way, my point is to thank. I was about to go-off half caulked and buy a bag with an unduely heavy shell fabric (no so smart as I think).

Thanks again

P.H.

I think I have sampled almost all possible light fabrics….Sure feel like it!

First, all the .8 , .85 and .9's, etc are really a bit heavier, usually 5-10%. It's standard practice across the industry to use the pre dwr treatment weights and even then it seems it is maybe taken from the lightest possible sample rather than the average. Ex: Lightest Pertex Quantum (non ripstop) now made is called .9 but final wgt is closer to 1.0. The older .8 thru-hiker was .9 and the new Momentum .9 is 1.05.(We only use final weights in our specs, risking wrong comparisons…)

A key factor to bag fabric is the air permabilty. I've tested some light fabrics that were .8 or .85 (really closer to .95 and 1.0) and they were light but so thin they were barely downproof and so the air permability was higher.

In a bag and bivy, the shell's air permabilty is part of the heat retention equation. You want it to breath enough to prevent condensation but not so much to allow heat to pass faster than necessary.

It's my opinion that using a very slightly heavier .95-1.0 (1 – 1.05 final weight) Pertex Quantum / thru-hiker Momentum) is better than a .8-.85 fabric (final weight of .9-.95) because 1: tighter weave and DWR application cretes a lower air permability 2: It's going to have amuch beter DWR for the .05-.1 oz/sq/yd weight and 3: It's going to be much tougher and completely downproof.

The difference in a bag's total weight between using a .85 and a 1.0 fabric is only about .5-.7oz.

I've stayed away from silk and the .8 / .85 fabrics for bags and bivys for these reasons. The .3 oz in a bivy top and .5-.7 in a bag is worth that extra weight in performance and durability.

As a practical test, when you put an ounce of water on the fabrics in a standing pool test, the .8 / .85's (older thin pertex, airlights, old thru hiker .8,etc) are OK but do start to soak through in a few hours and the .95/1.0's (new pertex quantum w/ mini ripstop and thru hiker Momentum) are totally bomber even overnight because or the tighter weave and better DWR treatments.

Summary:
Don't get caught up in automatically thinking a bag's or bivy top of .8 / .85 / .9 is better.

Paul and Ron,
I have to agree about nominal 0.8 for outer shells. I use it on the inside only. I should have said that. But the reason for using heavier fabric on the outside is not because of losing down.

I have made two quilts with 9 oz of 800 fill down in each.
One with the .8oz and one with the 1.1, both from thru-hiker.
Every statement from above is absolutely correct. The .8 fabric is much colder in the same temps from the loss of heat.
The Momemtum 90 works excellent as a shell, but you can't use it with the .8 since it's not sold any more.
When the .8 fabric is in humid conditions it is vary clammy any way. It obviously gains weight from your perspiration and condensation over the night, making the bag even colder.
Any one know how the Momentum 90 works as a liner?

Paul, I also have a hydrogen from back when they claimed it was filled with 900fp down. I don't really have any significant problems with quills poking out, but I don't use their stuff sack. I imagine that if you're using the factory stuff sack, which I feel is much too small and compresses the down more than it should be, the small number of quilled feathers would be forcefully pushed out the fabric by the compression. That's just my best guess, though.

-Eric

is it possible to purchase this same fabric somewhere?

Ron & Aaron (and anyone else w/direct experience)-

I don't quite understand the air permeability question on shells… It seems to me that if "X" inches of down is warm to 30*F that the warmth of the bag is dependent on "X," not the shell. Now, obviously if you were sleeping under a tarp, in an open-sided trail shelter, or an air permeable hammock then convection would be a problem. But if you were in a nylon-shelled inner tent it seems to me that air permeability of the shell shouldn't be a big deal. Isn't this kind of a "What weighs more, a ton of feathers or a ton of bricks" question? Won't "X" inches of down provide the same amount of insulation regardless of the shell? (Assuming you're in a protected tent or something, not under a tarp–or under a tarp, but in a bivy, etc.)

I'd greatly appreciate any insight or explanation!

Brad

Hi Brad

All sorts of things happen on the way to the Forum…

Suppose the shell was made of canvas. How much loft would the down have under that weight?

Suppose the shell was made of a plastic bag. How much moisture would accumulate inside during one night, sogging the down into an flat mess?

Suppose the shell was made of netting. How much warm air would you lose from within the down itself during the night asd you moved slightly?

Cheers