The Insulation Mess

Good post

The Mammut Sleep Well document talks about this pretty good:
http://www.mammut.ch/images/Mammut_Sleep_well_pt1_E.pdf

They talk about EN13537

They talk about comfort limit for women (similar to your warm sleeper), comfort limit for men (similar to your cool or cold sleeper), and extreme (survival). Lower comfort women and lower comfort (men) should approximately span the population of sleepers.

If you look at the plot on section 9, you can see that the lines for comfort women and lower comfort (men), have different slopes, but for zero insulation intercect the y axis at about 33 C (91.4 F). This means that all users have the same skin temperature (your base temperature) but men have a higher metabolism so produce more heat (slope of line is greater – thermal resistance vs temperature).

One small detail – I think 30% overfill is better for down. 10% not enough. This will keep your baffles filled without voids. If you overfill, you still get about half the warmth increase you would have got if you had let it completely loft.

I'll have to ponder the rest of your tables : )

Maybe "for dummies" it would be easiest to just say that 2.5 oz synthetic is good down to maybe 55F. 5 oz good down to 30 F. (or just look at ratings for Lawson's quilts). Adjust up or down 5 or 10 F if you're a warm or cold sleeper.

And, maybe 5 oz is too bulky so you want to switch to down. 30% overstuff. 2 inches of loft is about 30 F. 3 inches 10 F. Adjust by 5 or 10 F if you're a warm or cold sleeper.

I will definitely review the Mammut document- Thank you.

As for overstuff- in for a penny I suppose…
My recent thoughts on that in relation to a recent "failed" project, and where I get my 10% number from.
http://1drv.ms/1u28ozk
I would post directly but my carpenter brain hasn't figured out how to post a PDF here.

My "experiments of one" agree very much with your statement's-
As a warm sleeper- I find single layer Apex great in the 40-45 range.
Double or 5oz- a bit silly now since the availability of Water resistant downs has occurred. Prior to this though I preferred the moisture resistance at that potentially dangerous for down 30* range. Especially in the humid East/Midwest.
From there- down all day long for all the great reasons stated, once you've cleared 20* concerns of liquid water go bye-bye.

Exploring PL fills is an attempt to bridge that gap between Apex and Down as the murky area is encountered more often for me or the possibility of eliminating a shell causes reexamination of Apex and PL alternatives. I think many of us reach some serous head scratching between Apex for summer and Down for winter wisdom. You know- the old 35 and raining problem we all dislike :)

I see Zpack uses 30% overstuff

Yeah, that makes sense, baffle bulges so it's wider than design so requires more down.

If it's a horizontal surface, gravity tends to flatten it.

If you pull on the fabric sideways it tends to flatten the bulge.

In the center of a baffle, it only gets pulled from each side, but at the end of a baffle, it also gets pulled from the end – shorter baffles require more overstuff.

Measuring is only so accurate. Easy to get more or less down in a baffle.

The down isn't perfectly uniform. Some might have a little more or less loft than other.

The down can lose loft when it gets damp or if some leaks out over time.

So, it's way complicated – just overstuff 30% and you're probably good.

So, you say a little above 32 F, especially in humid conditions, down is not a good choice because down gets damp and loses loft. Maybe treated down is better.

I question that. I thought that, but then have been using down bag for about a year and haven't had a problem. If you sleep in bag, body warmth will actually dry out bag. The exception is long, cold expeditions. If freezing point is inside down, water will freeze there and not evaporate significantly. After days, your bag can gain a pound and become much less effective. This is for polar explorers, but few BPL people will experience those conditions. It has to be below 20 F (?) for days.

Down is, by nature, water resistant. Geese float around in the water and stay dry. Natural oils make it water resistant.

I've been using a modifed sewn through. I don't think I've convinced anyone, but if you make the baffles wider on the inside fabric, than the outside fabric, it will avoid the thin spots of sewn through seamed baffles. Cross section:

So, it's just as easy to make as sewn through (just one seam, no baffle strips to cut out) with the thermal properties of baffles.

Jerry,

I have thought about your sewn-thru method a lot in the past and see how it would work. My question (sorry if off topic) is, If I want a quilt to be 58" wide, can I do this design without piecing two pieces of fabric to reach this fished width for the inner layer?

Most fabric is ~60" wide in raw form.

Thanks,
Todd

Yar- I suppose the only insight on the overstuff question comes in response to claims made as to the benefits in increasing density of down to achieve higher warmth at a given loft. Some of the links you cited in your efforts spring to mind. I think that line of thought has some potential, my insight though is that you may need to look at very high levels of overstuff before you achieve those densities and that conversation can begin. I think in my geometry minded carpenter brain that a vast portion of that 30% OS is actually simple "fudge factor" used to correctly fill the baffle- so the density argument doesn't come into play until the baffle is filled to capacity to begin with.

Also covers all the items you mention and serves as a great "catchall" for these factors. Definitely exceeds my KISS starting point and the "Why/how" of overstuff is probably not needed for simpler discussion. But the density debate sprang up at HF and my thoughts spilled out on the topic.

My down opinions likely need a little updating as well. Shells and down quality are better than in my youth- so many of my down opinions need an update as well. To a certain extent my personal "speed hike" style of sleeping in crappy bivies or less than ideal conditions contributes to my outdated moisture concerns. These trips are typically longer than a week and moisture related loss of loft does come into play, always evident after a trip to the laundry mat on even fair weather hikes.

Nothing to back it up, but Geese spend a fair amount of time preening and maintaining that body oil. I would imagine most is lost in harvesting, laundering, sorting- but just a WAG.

I don't disagree with your sewn through design at all, in fact something like a WM highlite shows sewn through is not an entirely poor choice, as do most clothing items.
http://www.westernmountaineering.com/index.cfm?section=products&page=Sleeping%20Bags&cat=ExtremeLite%20Series&ContentId=16

That said, if weight were the concern over ease of construction I would note that the design would require about 1.5 times the baffle material to achieve (ballpark)but it may be worth running the numbers on for someone like me who hates making baffles.

If Jerry hasn't chimed in already- yes you'd likely exceed the 58" of fabric, but as you are already sewing at these points it should be little issue to add that one extra seam to patch the fabric together. If you wanted to keep is as short as possible you can use a 58" tall x whatever width piece you need and keep the seam parallel to the short side.

uh oh, you're encouraging me : )

yeah, like Bill said, you have to sew together two pieces.

You have to make one side pi/2 bigger. Actually, you can make it a little bigger or smaller but I think you want the baffle width to be about twice the loft.

Then, in reality it flattens a little – maybe 5%.

I made a test piece:

You can see that there is no thin place where the seam is like normal sewn through. There is a narrow slot of air, but if it's pointing inward, it will be against your skin, so will be about as good an insulater as if there was down. And if the baffles are pointing out and you have a windproof layer outside, same thing.

Looks like Western Mountaineering has regular sewn through seams. top and bottom fabric are the same width. Appropriate for a very lightweight bag.

I think you end up with same amount of fabric as if you cut seperate baffle pieces.

With box baffles, strips are the loft plus maybe 1/2 inch on each side for seam allowance. If you use my diagram above, that would be (B/2 + 1). With my technique, the extra fabric for each baffle is (pi/2*B – B) = 0.57 * B. For 6 inch baffles, that would be 4 inches for box baffles and 3.42 inches for my technique, so you actually use a little less, but it's not significant.

One other thing.

With regular baffles, the down tends to slide away from the front to the sides so on top of you, the baffles lose much of their loft. The marketing spinners tout this as an advantage because if it's hot you can let the down slide sideways. If you overstuff more it minimizes it…

On my next bag I'm going to do this:

Basically, do the same thing but at 90 degrees.

You put a fold at right angles and when you sew the baffles, just sew over the fold. Then put in down and fluff it until you're happy. Then sew along dotted line and down will stay on top.

The fold would have to consume (pi/2 * B – B) fabric.

Sewn through baffle? There will be cold spots.

"The marketing spinners tout this as an advantage because if it's hot you can let the down slide sideways."

I trust Western Mountaineering on this one.

Finally, should the baffles go inside or outside?

If they go outside, the slot of just air will be exposed to the air and if it's windy, it will get blown away.

But down is really susceptible to wind so you need an outer windproof layer to keep air from flowing out of the down, through the shell fabric, and away.

If the baffles go inside, pressure on the fabric will tend to pull the baffles tighter so you'll lose a little loft. If the baffles go outside, any tension on the fabric won't matter, the baffles will just sit outside and achieve as much loft as possible.

If you're a convex surface, and the baffles are on the outside, the slot of air will get slightly wider, which will actually provide more insulation. If the baffles are on the inside, the slot will get squished narrower

"Sewn through baffle? There will be cold spots"

Like I said, I haven't convinced everyone : )

Regular sewn through does have spots where the loft goes to zero. Asymetric does not.

Actually, it's more complicated than that. With regular sewn through, on your skin side, there will be a triangular air space, but since it's enclosed on all sides, there will be no air flow, so it's about as good as if there was down there. Same thing on the outer side if you have a windproof jacket.

But, with regular sewn through, if you put sideways tension on it, the baffles tend to get squeezed to nothing. With asymetric sewn through, one side takes all the tension so the baffles do not get squeezed losing loft.

I acknowledge this all is a bit unconventional so should be taken with skepticism.

Have you ever thought of making a hybrid with a thin layer of synthetic insulation with sewn through down baffles on top? Might be too heavy?

Initial thought- I see how shell weight could be reduced some.

Personally- if not in a bivy or cover- I think you have it backwards. You would want the solid shell out and the baffles in.
Two (mind experiment) reasons-
In the actual geometry of the quilt you would have no air pockets with it curved around you, the baffles would simply bump into each other if properly sized and filled. Done that way it's not really sewn through at all as you say, likely with baffles to the inside you'd get nearly a full height loft as the curve compressed the baffles into each other. If in a bivy shell, it might make sense to flip out- or even to "reverse" the quilt to intentionally reduce warmth on warm nights.

Also- In higher lofts especially- this greatly simplifies the differential cut problem for MYOG folks- you could do a simple offset of the outer shell relative to loft and inner shell size and provided you didn't blow it by anything crazy, the design would take care of itself in regards to maintaining an even cut over varied body geometry.

Have you ever thought of making a hybrid with a thin layer of synthetic insulation with sewn through down baffles on top? Might be too heavy?

Actually- that thought has some good possibility in an UQ application- where Synthetic could take the brunt of the weather/wind exposure and down could provide nice loft punch as well as fill the tricky geometry in an UQ.

"it might make sense to flip out- or even to "reverse" the quilt to intentionally reduce warmth on warm nights."

That would be a nice plus to Jerry's design. It would give the quilt a larger temperature range than other designs.

"You would want the solid shell out and the baffles in."

Yes

That's how I did it.

But, if you want an outer layer like a bivy, then you could have baffles out.

"Have you ever thought of making a hybrid with a thin layer of synthetic insulation with sewn through down baffles on top? Might be too heavy?"

What's bad about synthetic/down hybrid, is that synthetic loses it's loft after a few years, down lasts "forever"

"it might make sense to flip out- or even to "reverse" the quilt to intentionally reduce warmth on warm nights."

seems like you need to totally unzip or lower for warmest conditions

I have totally hijacked your thread Bill, but you are a contributor : )

Most of the quilts I use are easily reversible- In a true bag it would be tricky- but in a basic sewn footbox/drawcord quilt easy enough to do. Same on an UQ for a hammock. In my experience- I'm using these items for their versatility and temp range.
When it's really cold, I just bite the bullet and buy a good sleeping bag from an expert.

On the Synthetic/down combo-
When was the last time a MYOG tinkerer managed to use anything forever, LOL.
Not that I advocate "disposable" gear, it's just rare that I seem to make it more than a season or two without some new tweak or idea to incorporate. Discarded ideas go to the car camping/suitable for lending pile.

Down can be recovered at least if needed. I've had pretty good luck with APEX going a few good seasons, and even then, we're talking a 5-10 degree "downgrade"- or basically it gets added to that summer pile of lenders for when non-camping friends come out for a car camping weekend.

And yes- hijacked but not forgotten! I'd still very much like some more discussion on the original post- but I'm no stranger to the rabbit holes either, lol.

Good point, with MYOG seldomly does anything wear out before I get the itch to replace with some new thing.

"MYOG seldomly does anything wear out before I get the itch to replace with some new thing"

When I was 20, expecting to live forever, able to easily carry 70 pounds and poor I made and bought gear with the hope that it too would last forever.

Now at 69, facing the reality of actuarial tables, able to carry half the weight-half the distance for half as long, with more disposable income I'm very motivated to replace even new gear if something better comes along. If I waited for things to wear out I'd be dead before I replaced what I have. "Forever" has been replaced by the number of backpacking years I might have left.

If i ever make a down quilt, i would try out Jerry's asym baffle idea, as it seems like a relatively simple/easy fix for a problem. Maybe not ideal, or quite as good as internal baffles, but definitely seems a lot better than traditional sewn through.

"'Have you ever thought of making a hybrid with a thin layer of synthetic insulation with sewn through down baffles on top? Might be too heavy?'

What's bad about synthetic/down hybrid, is that synthetic loses it's loft after a few years, down lasts 'forever'"

There is a simple solution to this idea, take a down quilt, sew a single piece of super light nylon on one side with some overlapping fabric at the wide end. Within this "sleeve" sew some velcro at strategic points of the perimeter of the sleeve. Now take whatever thickness of Apex you like, cut to size, sew a small bit of super light nylon onto the perimeter that will match up to the places where the velcro is inside the sleeve of the down quilt. Sew the corresponding velcro onto the fabric on the Apex. Turn sleeve inside out, match up the velcro.

Voila, you have a super flexible, adjustable system wherein you can take out the Apex whenever you feel like, to replace once overly worn, want to boost to different levels, etc. All without having to unstitch the down quilt to add more down, or take a separate booster quilt which will ultimately weigh more because of the extra layer of fabric involved.

Remember Richard Nisely talking about Down jackets, and how a windshell over the outside of them, especially with sewn through baffles, boosted insulation up to 15% even without any wind, and more significant gains with wind?

Well, apply that principle to Down quilts. Not only extra insulation from the added layer of Apex, but also from that non sewn through "windshell" fabric over the top.

Generally speaking, you will want the Apex on top and not put too thick and heavy of Apex in, because it could compress the down too much, and you definitely want the lightest nylon sleeve material you can get for the same reason.

I think it's a great idea, but i'm biased as having come up with it. Above all, i most value flexibility and adaptability in my systems.

Some people put synthetic on the outside, so that the point where the temperature reaches freezing is in the synthetic, because water (ice) will accumulate there. This is only for real cold temperatures.

Yah, i know.

Bill – You have assumed that a given increase in Clo will give everyone the same increase in temperature rating. I don't think this would be the case.
A cold sleeper generates less heat (by definition). Thus, he or she requires more insulation. Obvious enough. But I believe it follows that the cold sleeper requires proportionally more added insulation as well to achieve a given increase in temp rating. So while your chart assumes that 2 clo adds 20 degrees for everyone, I think that really if 2 clo adds 20 degrees for the warm sleeper it would add less for the cold sleeper.
Think about it this way – per your chart, the warm sleeper needs triple the insulation to keep warm at 50 degrees (3 clo vs. 1 clo). But at 0 degrees, the cold sleeper would only need 1/3 more (8 clo vs. 6 clo). That does not seem right to me, but perhaps someone with more thermodynamic chops can explain how it should be.