The Insulation Mess

I think that you are trying to apply a ratio type relationship where I understand it as a linear one. It looks like the cold sleeper is always 2 CLO behind, so as CLO increases the ratio gets out of whack.

I think that matches the EN rating system well enough or simple conventional wisdom. As mentioned, High school math was the end of the line for me, so I don't know much about relating and graphing the numbers.

It's definitely only meant as a good jumping off point for MYOG really. Easy enough to pick up a 32* bag off the shelf, a little harder to hit that mark ourselves. Or just as important- if we know that a commercially rated bag is X* and we need X =/- so many degrees for our personal comfort then we can make that adjustment too.

Bill,

The warm, cool, cold classifications also apply to individuals (at least for me) on different nights, depending of how one feels, hydration, nutrition, etc. I also see (again just for me) a change during the night. I typically sleep 10-12 hours per night when backpacking. I love to sleep. The Daryl that went to sleep in the evening after an active day might be classified as a warm sleeper. The Daryl that is trying squeeze in a few more hours of sleep at oh-dark-thirty in the morning has been dormant for 10 hours or so and could be classified as a cold sleeper.

Daryl, so what? What's your point?

Well, because of this individual variation I tend to err on the side of bringing a bag that is a bit warmer than I need. It terms of the chart I would always assume that I'm a cold sleeper.

It's a slope difference

degree F per CLO is more for a cold sleeper

maybe you're making it too complicated:

for MYOG, 2.5 oz Apex is 55 F, 5 oz is 30 F, etc. for average person

2 inches of down with 30% overstuff is 30 F

this assumes you wear some insulation inside

if you know what works for you, you can adjust. e.g. if 2 inches of down + 1 inch of insulated garment inside = 3 inches total, is only good for 40 F for you, then it's (93 – 40) = 53 per 3 inches = 18 F per inch. If you want to lower 18 F, add 1 inch.

I'm not sure which Daryl I'm talking to, but

You have to use your sleeping bag/pad/other stuff you're wearing, on a number of trips.

For example:
If one night it was 30 F and I was comfortable,
another night 35 F I was comfortable,
and a third night it was 30 F and I was uncomfortable
then my lower limit would be 35 F.

The more nights, the more you can dial it in.

Actually, the temperature to use would be what the weather report says. I always check ahead of time, find the coldest temperature it will be, and then make sure my gear will keep me comfortable at that temperature. You also have to factor in the inaccuracy of weather report.

Jerry,

Good points. Actual experience is the key for me and Daryl too.

Yar- the underlying motivation for me is to maximize synthetics. The one layer, two layer Apex isn't working for me, so temperature bridging materials like PL have some appeal. I am tinkering with down, but typically will rely on commercial sources- I have a 32, a 10, and a -20 bag in down. And when it's truly cold, I don't play around much and have a different style.

There are a lot of reasons though that Synthetic makes sense for me-
I go with the "just get wet" school of thought while moving, as I sweat myself out anyway in all but winter conditions. As a result though, I often crawl into bed damp, or even wet. I may also rely on my sleep gear if I get into trouble or need to dry a baselayer or socks.

As overall gear weight and volume have decreased-
I don't need the compression advantage of down, in fact, the loose stuff synthetic does a better job of filling nooks and crannies and stabilizing a load without relying on compression straps in my pack design. Leading to an overall lighter, less complex system.

I often camp "dirty" throwing down in less than ideal conditions or in poor weather and don't take the time to care for my gear. On multi-day trips this leads to damp or even wet gear. Something that seems to affect synthetic's very little in my experience.

The advent and availability of water treated downs though changes the argument somewhat, and a pack can easily be remade to take advantage. While I have little practical experience with the treated downs, feedback is positive enough to assume that my damp (but not soaked) style may be compatible.

The question now-
What synthetic styles and fill combos will give me the more elusive three season bags/quilts.
And will they be similar in weight to down at these 25-55* ranges- a range I think we can all agree on it's hard to get efficiency and proper loft from down.
Finally- could the proper design/technique (a bit like Jerry's idea) produce an effective bag for this range when paired with WR downs?

I have a failed down experiment in a 1.5" baffle bag 5" wide design. Even with 30% overstuff it is listless and shifting. this includes a few grams and eyeball pinches extra along the way. This bag could be made to work with more fill, but it is already heavier than the synthetic equivalent. Same with a tighter baffle spacing, a 2.5" wide baffle might constrain and loft better, but at the cost of complexity and weight.
This failed project led me to the overstuff insight I posted earlier, and what I believe was the cause of the 30% OS failure, 25% of the fill likely was just that, another 25% may be needed just to reach expected performance/overstuff benefits.

The bottom line being- that 40 or 30* down isn't that great either, it's just not enough volume of fill to reach peak performance of down.

A 3.0oz PL and 2.5 oz Apex combo though may prove a better solution overall. Or even a straight 4.0oz PL style if it can be worked out. The Double layer Apex is decent- but you are stuck in the 2,4,6,8 CLO formula if you stick with Apex. And it is heavy/bulky enough to seriously consider a "better safe than sorry extra layer"

I think we all agree-
Summer- a simple Apex quilt is great, simple, light.
Winter- get you some geese and bundle up.
In between is in between- You either go better safe than sorry and bring that warmer down bag, or take a bit lighter or underrated Apex and pile on the hats and clothes.

The flaw for me- I don't need the clothes for anything but sleeping- so that old standby is inefficient for me.

So for the hell of it I sketched this out. The perimeter is within a 1/16" in each shape, close enough for me. So what this shows is the deformation that should happen in a few different scenarios right?

For giggles- the .7 sq in difference over say an 80" long baffle would be 56 cu in.
10 baffles on a 50 inch wide quilt- 560 cubic inches.

if we round to 9 sq in as a base number- 9*80*10=7200 cu in of fill.
The little slop above- 560/7200 is 7.8%

Admittedly- the difference is not too large in area, certainly much tighter than the standard rectangle vs baffle shape before (25%).

But which area to use, and what would be fill, what would be overstuff?

The promising news-
The baffle shape/design leaves much less room for error in fill or stuffed baffle area.
The construction is much easier.
The baffle material is at least equal, if not reduced depending on what profile you "pick"
Design simplifies differential cut considerations?
You should be able to keep baffle spacing relatively wide?

The bad news?
It's hard to say what shape the fill will actually take- so the total loft is a bit unpredictable.

Thoughts, errors, corrections?

So you go directly from hiking to inside sleeping bag, and vice versa? I like to hang out for a while so some insulation is good, which I then wear inside sleeping bag. While I'm hanging out for a couple hours, eating, drinking some adult beverage, my wet clothes will dry.

PL1 is maybe 10% more warmth for the weight. But the extra quilting required is a pain, hardly worth it.

I made a bag that was maybe 3 oz primaloft or polarguard. Not warm enough.

I made a bag that was 5 ounces Apex. Still not warm enough – I want to be comfortable down to 20 F. Plus, it is so bulky in my backpack. And the tighter you stuff it, the shorter the lifetime.

I was afraid of down, but construction isn't that much more difficult – either regular baffles or my idea. With reasonable precaution, I haven't found that getting wet is a problem. Stuffing the down isn't that difficult – easiest to just weigh it with 0.01 oz/0.1 g scale, grab between fingers and stuff into baffle.

I have 2 inch loft with 4 inch baffles. Used for about a year. Worked pretty good, except I used Nobul1 which leaks a lot of down. It seems like over time it's been leaking less – maybe just the feathers leak and the down stays inside?

1.5 inch loft and 5 inch baffles? My theory is baffles should be twice the loft – so you should have 3 inch baffle instead of 5 inch. When you make it bigger, it's more difficult to avoid voids.

owfinc has 2.2 and 6 oz Apex, also 3 oz Climashield which I bet is pretty much just as good. thruhiker has 2.5 and 5. I used 2 layers of 2.5 to make 5. You can make pretty much anything you want. The 2.5 oz is probably 2 oz some places/lots and 3 oz others.

I think the only time synthetic makes sinces is like 2.5 oz summer, except it has to be replaced after a while so it's hardly worth it. Otherwise, down is lighter. You can just use your 20 F bag even if it's 30 or 40 F and it would still weigh less than a 30 F or 40 F synthetic bag.

just looking at my 2 inch baffle/1 inch loft test piece, and 4 inch baffle/2 inch loft bag, the top flattens, not the sides:

Maybe you have 5% less cross sectional area. I just ignored it – did 30% overstuff, so maybe it ends up being 35% overstuff in reality. This is about my measurement error.

A big thank you for talking this out/working on it. I think you have something and may want to try- just trying to wrap my head around it. Google sketch-up let's me do math I wouldn't otherwise be able to. Hope this doesn't feel like an attack on you or your ideas in anyway- it is not meant that way at all.

So a flatter top (which makes perfect sense) looks like-

I am basing this on the perimeter- which cannot change- all shapes have the same perimeter (+/- 1/16)-
The two new ones have a flatter top, including reversion to a full rectangle. The area reduction gets worse compared to the cross section at start, but I think the Pink shape is the one you have in mind and best matches on the eyeball scale.
In your first sketch you show a B/2 x .95 for height of baffle.
The pink shape is an average of 1.46" ((1.25+1.25+1.875)/3)(ASSUMING THAT IS RIGHT)
So the actual height would be B/2 x .58 correct?
Actual area- 9.7 vs. 8.34- a built in OS of 16%.
FWIW- with baffles to the inside, I agree with the theory of increased volume of conditioned air- so the absolute loft may not be accurate- but still close?

Let's call it 1.5" of loft. Equal to 2 CLO (Apex 2.5) on my chart if that's right?
Forget temps as they are relative to the user right?

50"x80" quilt- 3.08yds per layer. Argon/M50 Shell- .67 oz/yd2

Apex- 6.2yds shell, 3.1yds insulation (6.2*.67+3.1*2.5)= 11.9 oz.

Down-
per 5" baffle- 7.875" second shell. (rounded up 1/16)
Outer shell- 50" 3.1yds
Inner shell- 78.75" 4.86 yds
((3.1+4.86)*.67) 5.34oz shell total.

Fill- lets do 850 with 30% OS.
Your formula- 9.7sqin x 80" x 10 baffles/850x 1.3=11.86
My theoretical area (pink) 8.35 sqin x 80" x 10 baffles/850*1.3=10.21 oz

Finished bag- 1.5" loft
Jerry- (11.86 down plus 5.34 oz shell)17.2 oz
Bill- (10.21 down plus 5.34 oz shell) 15.55 oz
Apex from above- 11.9 oz.
Adding a second layer of 2.5 apex for fun- (11.9+ (3.1*2.5)=19.65 oz

I think the loft adjustment in your first formula is the issue? Or the error simply lies somewhere on my end and can be corrected and make me a happy fellow- because I like your idea very much! I just can't get the numbers to work right.

Oddly- this is almost the same results of my recent (first) attempt at MYOG down.
(a 5" wide x 1.5" tall baffle) shape and features similar.
The apex quilt came out around 11.25, the down is at 14.25 and still could use another 2 ounces of fill or serve as a high maintenance (re shifting down all night as it settles) bag.

My favorite post from BPL was when Daryl said "can we get back to talking about me?"

Us old people are just glad to have someone that will listen to us : )

And back when I was working, people attacked each other a lot more vigorously than your mild questions. : )

The design height (loft) for 5 inch baffles should be 2.5 inches

In actuality it collapses to maybe 2 3/8 inches

But I just noticed it poofs out the bottom about 1/8 inch. Like you were talking about with regular baffles.

Since we don't know what actual shape it is, there's hardly any point assuming some shape and then calculating the cross sectional area of that. Since the half circle collapses a little, that will slightly decrease the cross sectional area. Since it poofs out the bottom, this actually increases the cross sectional area a bit. I don't really see any point in calculating. Just use the design shape – a semi circle. Then add 30% overstuff.

I have a 5 oz Apex bag – comfortable down to 30 F.

I have a 2 inch loft bag, 4 inch wide baffles – also comfortable down to 32 F.

Assume 3.1 yd2. 5oz Apex is 15.5 oz of Apex + 4.1 oz Argon = 19.6 oz – as you said

With down, assume 2 inch loft just for apples to apples. 3.1 yd2 = 4018 in2. * 2" loft = 8036 in3. If you want, remove the space between baffles that doesn't have down. The area of a semicircle is pi*r^2/2. The area of the rectangle is 2*r^2. The ratio is pi/4. So the volume you want to fill with down is 6311 in3. Add 30% overstuff = 8204 in3. 850 down = 9.6 oz. The fabric is 3.1 yd2 on one side and 3.1 * pi / 2 on the other side (regardless of loft) = 4.9 yd2 = 8 yd2 total * 0.67 oz argon = 5.4 oz. Total weight is 14 oz.

sigh…
I'm with you most of the way (I think)

The only thing I still take some issue with- is measuring the actual loft of the bag. On a flat surface given the same perimeter of the half circle, as it deforms or flattens it's height has to go down a decent bit, maybe 25%.

That said there are two things opposing this that likely explain it-
The fill power and pressure of the expansion prevent the collapse and-
once formed into a curved shape the distortion "evens" it out anyway.

You have a working 2" full size model? I had thought you only had the pillow samples initially because of the pictures but re-reading I wasn't sure.

And regardless of my quest for the WHY- it seems that it works in practice, which is ultimately all that matters. (I did just build a quilt that should work in practice but didn't so a bit gun-shy, lol. But I agree the baffle spacing, not the fill is likely the issue)

So the math that seems to work-
H= design height- Final loft is…some percentage- 95% is where you are at now.
H x 2 for baffle width.
Width x pi/2= width of rounded shell.

Fill- You lost me a little there-
simple is best- Area of project x final loft x 30%
Or do you not add the OS if you don't cut out dead space? I assume you meant the first formula is what you use and meant to add OS from previous posts and just omitted it here on accident…

"3.1 yd2 = 4018 in2. * 2" loft = 8036 in3. {+30% MISSED?}

If you want, remove the space between baffles that doesn't have down."

I made a hybrid quilt/bivy that I've used for about a year – 4 inch baffle spacing, 2 inch loft

and a 12 inch square test piece – 2 inch baffle, 1 inch loft

pictures of test piece which is easier to examine than the quilt

top:

You can see the ends of the ruler line up with the row of stitches that are the sides of the baffles. The fabric actually sticks out a little more. 6 baffles. so, 2 inches per baffle. I cut the longer side to be 2 inches * pi / 2 = 3.14 inches per baffle.

edge:

I tried to line up the center of the camera lens with the top surface. It's hard to see any flattening of the semicircle. So I'm changing my mind, it's not 0.95. Best just to assume a semicircle. If you push out with enough force, it wants to assume a semicircular shape.

It also puffs the other side about 3/8 inch. More than I thought before, but upon this closer examination…

other side:

hmmm… I'de say it flattens the sides a little like you said in the first place, and the top is flattened. Yet when I measure it, it's still 1 inch loft. The more I look at the piece as I rotate it around and look at it edge on, the more it looks like a semicircle with very little flattening. Hard to get good picture.

3.1 yd2 = 3.1 * 36 * 36 = 4018 in2

loft is 2 inches so the volume (ignoring the empty spaces outside the semicircle) is 8036 in3.

next I removed the volume of the air space outside the semicircle, but I'm now having second thoughts about doing that. If I ignore this, it will make up for the amount the baffle poofs out a little on the other side.

next do the overstuff, so multiply the volume by 1.3. 8036 * 1.3 = 10447 in3. That's how much down we want.

next, calculate how many ounces of down are needed. using 850 down, divide the volume by 850. 10447 / 850 = 12.3. so, you need 12.3 ounces of down.

I just looked at my test sample. 12 inch square, 1 inch loft, so it has a volume of 144 in3. overstuff by 30% so use 144 * 1.3 = 187 in3. 850 down, so 187 / 850 = 0.22. I should have used 0.22 ounces of down. Actually, I used 0.24 ounces of down. My scale is 0.01 ounce resolution, and I weighed the down for each baffle. 0.22 / 6 baffles = 0.03666 ounce per baffle. I rounded up to 0.04 ounce per baffle because of scale resolution. 6 baffles * 0.04 = 0.24 ounces total. I weighed it before I put the down in, and after, and subtracted, to check the weight of the down.

Any clearer? Sorry to keep changing my mind : )

So to do apples to apples comparison

Apex – 3.1 yd2 – 4.1 oz for fabric, 15.5 oz for apex, 19.6 oz total

Down – 3.1 yd2, 2 inch loft – 5.3 oz for fabric, 12.3 oz for down, 17.6 oz total

Yeah, when I used them they were both good down to about 30 F, but I measured them more accurately than that.

Apex – 2.05 clo, down – 2.81 clo

For apples to apples comparison, I would only need 2" * 2.05 / 2.81 = 1.46" loft down

In this case, I'de only need 12.3 * 2.05 / 2.81 = 9 oz of down, so bag would weigh 14.3 oz total

14.3 / 19.6 = 0.73 – down is 27% less weight

I am now thinking I want a bag twice as warm – 10 oz apex. Apex bag would weigh 35.1 oz. 2.92 inch loft down (actually I'de do 3 inches) so 23.3 oz total. 23.3/35.1 = 0.72 so I'de save 11.8 ounces or 28%. But a 10 oz apex bag would require a ridiculously big pack – I'de never do that, but this is where down really makes sense. I could use this down bag even if it was warm – just don't zip it up. A 2.5 oz apex bag would weigh 12 ounces total. So maybe it makes sense to have a 2.5 oz bag for warm weather and save a little weight. But a 1.46" down bag weighs 14.3 ounces, a little more, but is twice as warm, so maybe that makes more sense for warm weather.

One other thing, on my bag I have 2 inch loft on the top half (torso) and 1.5 inch loft on the bottom half (legs). The legs have less surface area skin and you restrict blood flow to them so the skin temperature is a little less, so if you shift a little insulation up to the torso, it saves a little wieght/is a little warmer. My bag is about 1.5 ounces lighter without losing much warmth. Maybe this adds too much complication without saving much weight.

Thank you!

"next I removed the volume of the air space outside the semicircle, but I'm now having second thoughts about doing that. If I ignore this, it will make up for the amount the baffle poofs out a little on the other side"

This is the only thing I question too. As you see- the down's expansion force is what is allowing it to keep it's shape, so any attempt at a "perfect" fill won't work, that's what I tried with my last bag.

It may be the angle- but you may even have a hair over the 1" design- so there is no reduction in design height at all (good news)- and you can claim the full loft intended so long as you calculate for a full height with nothing removed and add the overstuff too.

So what ever you choose H to be…
Fill the rectangle at the full height of H + 30% OS.
Does that match the full size you have?

That number makes more sense to me- and roughly matches the 30* breaking point I come up with… This bag, fully filled with 850 would be within an ounce or two of the double APEX. That's fine. That weight is in line with other bags of that loft, maybe even a hair lighter. It's a slightly more predictable shape and easier to build.

What is the "max" with this (I know it's just theory) Does a 3" or greater make sense, or do the chambers get so big that down movement inside is likely?

yes, just use H, multiply by 1.3 for overstuff. That's the same as if you used conventional box baffles.

I don't think there's any max limit to down bag. Make it as big as you want. At least there's nothing limiting in a size you'de ever do.

"It's a slightly more predictable shape and easier to build."

The break even point would be about 1 ounce apex. 4.1 oz for fabric, 3.1 oz for insulation, 7.2 oz total. 0.29 inch loft down, 5.3 oz fabric, 1.8 oz down, 7.1 oz total. But that's a ridiculous example – too many baffles and they don't make apex that thin and it's not warm enough.

Maybe the more resonable "minimum" is 2.5 oz apex – 11.9 oz total, or 1.46 inch down – 14.3 oz total, but it's twice as warm as the apex.

I don't know that apex is easier to construct. Sewing through fabric/apex is a pain. As you're sewing along, the apex gets hung up on the pressure foot so it slide relative to the fabric. Especially if you use the asymetric sewn through baffles, it's not that difficult to do down. But box baffles aren't that difficult either – cut a bunch of strips, sew twice as many seams as asymetric.

Stepping out of your idea for a second and back to the Original Topic-

I think I have the overstuff insight I was truly looking for. Forgive my pretend scientific paper presentations-

1- Nylon is a non-structural material, in that it is not rigid and cannot hold a shape.

2- Down is "an equal opportunity expander". The ideal final shape being a circle.

Observation-
Regardless of baffle design or intended shape, provided enough down is available it will continue to expand an individual baffle until it creates a circle. The adjoining baffles or overall design prevent this tendency to some extent.

Goal-
The "ideal" filled bag fills each chamber to it's maximum volume without using excess material

Theory- proposed formula-
Overstuff is a guess, and varies by large amounts even between "pros"

If a nylon baffle was filled with unlimited down, it would deform to a circle.

This circle would be equal in circumference to the perimeter of the sewn baffle.

Therefore the correct amount of down to fill a baffle is equal in area to a circle that has a perimeter (circumference) equal to the perimeter of the intended shape.

You have Jerry's 4×2 baffle- 6.2 sqin
The rectangular fill used- 8 sqin
The matching circle to Jerry's baffle (perimeter=circumference)at 8.25 sqin
And for fun- the circle matching the rectangle at 11.33sqin

8/6.2= 1.29- baffle to rectangle
8.25/6.2=1.33- baffle to equal circle
11.33/8= 1.42 rectangle to matching circle
(makes sense as the adjoining baffle and design of a typical down bag restrain the full circle forming- as in why 30% works)

in the previous post-
going from semi-circle to rectangle- is 30% overstuff.
But going from semi-circle to rectangle AND 30% overstuff is (8*1.3=10.4/6.2)68% overstuff compared to the original semi-circle…
Maybe why you were waffling on adding that last 30% that I may have talked you into?
If you did 30% above the semi-circle- that actually puts you within a percent or so of my theory above, especially as your shape is already half circle.

It also explains why my project (1.5" x 5" tall rectangle baffles) is not full.
2×5= 10 sqin, but 14/PI= 4.46" diameter circle with an area of 15.45 sq in- 55% overfill needed for optimal fill.
(Discounting of course the bag would have been bad because the baffle spacing was too big, BUT it would have been full!)

That sounds reasonable – yeah, nylon not stiff so wants to assume circular shape

But then baffles should be perfect circles – baffle width = loft. That's what you get with symetric sewn through baffles. But, like I said before, then if you pull on the fabric sideways to the baffles, it tends to squish the baffles so you lose loft and therefore warmth. That's the problem with sewn through, not cold spots. But I haven't heard anyone else talk about this so maybe I'm off in left field : )

With box baffles, you mostly avoid this squeezing baffles losing loft when you pull on it sideways. With asymetric sewn through you avoid this even more.

I think the 30% overstuff is:
verified by experience – when people don't do this, they tend to get voids, but probably 20% would be okay too
makes up for errors in putting down into each baffle – if you screw up and put a little less into one baffle it doesn't matter
if the down loses a little loft because it's damp or dirty, you'll still avoid voids
If you put more down in without increasing loft, you still get half of the warmth increase you would have got if you had let it loft perfectly, so you don't lose that much.

My chart shows 1.5" loft as equal to 2CLO= to one layer Apex.
Although I note that perhaps I should slide clo over to the "cool sleeper" category, and that would put one layer of Apex at 50* vs 40* and line up better with "average" performance. I have no issue with Apex to 40* personally, but I see many do. The math I do not have is LOFT- CLO, that conversion is likely off 10* on my original chart as I am a warm sleeper and "good" with Apex to 40* personally.

From Zpacks site-

Does anyone know LOFT TO CLO formula, or even rule of thumb? The Zpacks chart is a BPL chart. Although comparing it to Tim @Enlightened Equipment it looks like his 2,4,6,8 ratings equate to 50,40,30,20 using 2.1 (1.77CLO per layer) http://www.enlightenedequipment.com/prodigy/

So I finally understand your point! Thank you!

Construction is debatable as well, but my thoughts/experience-
All of the materials discussed are hard to sew. Argon a bit less slippery than M50, M50 as slippery as 1.1 Sil. All easy to loose your line or have layers not line up.

So any stitch is hard to sew, especially as they get longer and longer.
You have to sew the perimeter of any bag, true you might futz with that seam in adding a layer of APEX, but once done, it's done.

more or less- you have much fewer linear inches of sewing to do overall, and technically you would have sewn the perimeter regardless, even if you have to go a bit slower.

Apex- Cut shell and Apex, sew perimeter and done.
Down- Cut shell,(cut baffles or not) Layout all seams, stitch all seams, sew 3 sides, measure down, stuff down, sew final side, spread down.

Maybe "harder" isn't the word so much as more time consuming, more steps, more lineal inches of sewing, more room for errors, etc. I do production work, so "moves" are something I analyze often. Start to finish I can do an Apex quilt in roughly 1/4 of the time as a result. Not that it's a huge factor for MYOG, just something stuck in my mind probably best left out of the conversation.

Yar, it isn't that overstuff doesn't work- just that the "why" bothered me.

I also have a bit of a beef with it as well from a marketing/consumer standpoint.
If I pay a pro for a perfect bag, I should get one- and if we all agree down lasts "forever" then why do I need to pay for more fill? I also expect a pro to do better than 30% margin of error.

Part of it is gram weenie tendencies and simple "getting my monies worth". I recall BPL posts debating shell vs fill weight ratios- for MYOG that is a meaningless conversation if you can't accurately determine fill or if you try to push to "zero" wasted weight. How could you come up with that "ideal" shell if you don't know it's volume.

Part of it is what I long suspected- OS is not overstuff, it is simply stuff, and nobody knows exactly how much fill is needed. If it was a real number, rather than a well informed guess, it would be uniform across all vendors.

It also makes for expensive experimenting when trying new designs or shapes, especially in my case where weight on paper is part of the process. This gets worse when looking at quilts with head to foot tapers and the resulting tapered baffles.

Again, thanks- love to hear more folks weigh in. I know it's a nerdy exercise hunting down the great WHY, but that's what this site is supposed to be.

The best clo to temp is Richard's chart http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

The MET=0.8 line is what to use for sleeping. That might be conservative. That includes sleeping bag and anything you're wearing inside.

loft vs clo is variable. Depends on which type of synthetic or down and if the down is fully lofted. That sort of led me on my quest to measure it. What I measured:
clo oz/yd2 clo/oz/yd2 loft clo/inch
2.5 oz apex 2.05 2.42 0.85 0.7 3.07
3 oz PLOne 2.18 2.42 0.90 0.7 3.25
30% OS 850 down 2.81 2.07 1.36 1.1 2.51

So, loft to clo conversion:
for 2.5 apex – it's 3.07 clo per inch
for PL One – it's 3.25 clo per inch
for 30% overstuffed 850 down – it's 2.51 clo per inch

if you overstuff down more, the clo per inch will increase

I wonder about other than 850 fill power down?

If you look at zpacks table, 50 F is 1.2 inches, 15 F is 2.4 inches (interpolate), so 85 F would be 0 inches.

This is inconsitent with Richard's chart which says about 93 F for 0 insulation. Maybe 8 F difference is small enough to not worry.

Richard's chart is consistent with EN13537 which also is about 93 F for 0 insulation. When I'm a bit cold at the end of a night, I measure my skin temperature at 93 F. I think that's a better number. I don't trust that earlier BPL article, but it was close.

And the slope – if you subtract 50 degree loft (1.2 inches) from 0 degree loft (3 inches) that's 1.8 inches per 50 degree F, Richard's chart is about 5 clo per 50 degrees difference. If you use my 3.07 clo per inch, that would be 1.63 inches per 50 degree F which is close to zpacks 1.8. So the zpack chart (older BPL article) has an x axis intercept that's a little off, but they make up with it with a bigger slope, so it's closer at typical temperatures.

Probably too obscure : )

Are you saying Tim uses 1 layer of 2.1 oz apex for 50 F, 2 layers for 40 F, 3 layers 30 F, and 4 layers 20 F?

I'll have to dig into that stuff- but to answer your question- look at the prodigy specs. Generally BPL customers call them conservative, but in reading the Mammut document most BPL members would be "experienced" users and closer to the bottom of the EN ranges.
http://www.enlightenedequipment.com/prodigy/

About matches your thoughts above- Call it 2oz and about .5" thick- (2oz*.82clo/oz*2) would give you 3.28 clo per inch or so- even with your 3 after a little wear most likely.

I lost you a bit for sure, but will re-read for sure. I'm not a fan of the CLO per inch variant of things. I think and want ounces of warmth- I have yet to see that the higher density pays off too much. Happy to hear otherwise, but IIRC, that argument went over even less well than your baffle idea :)

93* as an EN base makes sense- they say that's the temp you won't sweat or the upper limit correct? 85 being the temp that a cold sleeper would wake up- or basically your starting point for the women's comfort rating right?

What I used to tell folks when I sold gear was to check the house thermostat after they fell asleep for a nap- use that number as your base number.

To me 85* seems conservative at first glance, but as a warm sleeper with a base closer to 70- that 10ish degree spread in the Women to Men's comfort is about right. I like the EN system overall.

The rules of thumb I have heard (likely via Richard and BPL)
1 CLO =10 degrees
1/4" down loft = 10 degrees

But though that holds up- if you try to apply the rule to Apex it doesn't exactly work. 85* -(2CLO or 20*) means that a 2.5 apex quilt is only good for 65* for women and 55* for men? Although…the extreme limit takes about 20-25* off that number- say 35*

So EN for APEX 2.5 would be 65/55/35? Maybe…
I fall in the warm/experienced sleeper category- no real complaints around 45- and I know for a fact that 35 and soaked is the limit.

But you can't ignore the word of mouth and other field experiences that probably agree to that rating within 5deg or so. But the prodigy is a well rated and oft used quilt, Tim ain't exactly a shady vendor either, lol.

Apex 5.0- 45/35/15
Then if I am getting things right?

Fill- Another pet theory- 850 is probably a practical limit. In my limited experience with some of the 900/950 fills I have seen- it almost seems as if you get to a point where there isn't enough "stuff" left. That the material itself is stretched too thin to support itself so to speak. A bit like how poor density foams don't perform as well no matter that they are 1/8" thicker. Pet theory only, so pet it at your own risk and beware of fleas.

"Tim ain't exactly a shady vendor either"

I think Tim makes excellent quilts, based on comments here. And if he sells a 30 F quilt and people are happy, that experience is better than any theory. I am not questioning Tim or any other equipment maker or anyone that tests stuff for a living.

I'm just trying to figure out why and so forth. And trying to be able to make my own sleeping bag without having to make a bunch of expensive prototypes in order to dial in what I want.

93 F is the x axis intercept of Richard's plot, and the EN13537 plot (I think their plot has temp on y axis, but whatever). That is, the temperature for insulation = 0 is 93 F.

When I have been sleeping and I'm somewhat cold but still (barely) comfortable, I've measured my skin temperature to be 93 F. Core temperature is 98.6 F. There is some insulation from the skin and tissue, for example blood flow to skin is reduced when you start getting cold.

I think that's the "why" for the x axis intercept being 93 F.

When you're sweating, I assume the skin temperature is closer to 98.6 F.

If you're sleeping naked and it's 85 F, I think you'de get uncomfortably cold. If it's 93 F you'de be just a little cold.

Richard's plot – yes, 1 clo is 10 degree F. But I think down is 2.5 clo per inch so 0.4 inch would be 10 degrees. I think synthetic is 3 clo per inch so 0.33 inch would be 10 degrees.

I think there's legitimate 900 fill down that's better than 850. The main thing is to remove all the feathers. And maybe the down clusters are better on some birds? Yeah, probably easier to compress higher fill power down?

LOL, my apologies.
I wasn't implying that you were implying anything against Tim or his work.

It just seems that there is some "X Factor" in Apex that allows it to perform a bit better in the real world vs. the lab. EE's ratings and happy customer base being an example of this.

On the down- the only way my carpenter brain can work it out-
Say you have an ounce of paper pulp, and form it into a cylinder of 3". Then you make that out of cardboard, plain paper, and tissue paper. The pulp is your "stuff" and despite the strength of the base shape, at some point as your cylinder gets taller and taller you cross a line and your stuff is spread too thin to do the job.

That's the way I think of down, at some point the stuff that forms the clusters is spread so thin that it can't hold it's structure. As all the bags we make require that structure to exert force on the shell constraining it, (as well as all the other real world problems) there is some balance point reached.

Too much has flown through my head, but I think Roger or Richard may have also discussed this a bit at some point. Also, since we are talking stuff in relation to volume- as the stuff is spread bigger and bigger- air is the only thing to fill it. If the trapped air has too much space to move, then convection loss increases even in still air.

So then you are back to increasing density to increase CLO, which may indicate that at the highest fills, there is too much air at "perfect" density relative to max loft(900 fill filling 900cuin). Too much cold air allowed to fall amongst the rising hot air? So doesn't an 850 using the same amount of "stuff" increase density all on it's own naturally? With the added bonus of increasing wallet density to boot, lol?

Being in construction I think of it a bit as how the outer surface of a wall and inner surface of a wall find the temps meeting in the middle somewhere inside the wall, in a house this creates moisture issues since that "line" is deep in the wall relative to the outside face. There is a big push in construction to move insulation further and further out to reduce the moisture infiltration issues. I have seen some wall assemblies with little or no stud bay insulation and several inches of foam outside lately, and a push away from traditional batt insulation all together. No micro air currents in foam…

So I picture down as much the same, where too much free air leads to that cold layer being closer to the body, essentially negating some of the loft in the highest of fills. No real evidence on my part, just pure speculation. But in looking at some of the latest 950 or even 1000 fill down garments, I think we can agree that most users were not too happy…if fill was the only part of the story they should have been wildly successful for the gram weenie or innovation chasers. I also note that Patagonia's recently redesigned down line uses 600 and 800 fill again after pushing to 900. (Of course this could be simply explained by their move to traceable down, and that supply chain not being able to meet demand in Higher fill powers.)

Perhaps the "X factor" in Apex or PL is the higher/more uniform density doing a better job at keeping the break point further from the body, resulting in a bit more effectively conditioned air per ounce of stuff or even relative to loft. Perhaps it performs as hybrid between dense CCF and lofty down.

My head is not ready for CLO/oz at the moment- but your explanation of the base temps is appreciated and understood at least. Somewhere in there- the baselayer put on the manikin likely accounts for a bit of slop in there to get the temp slope going, but my brain is not working well enough on that count right now. I think you are on the right track ignoring "zero" for now and focusing on the changes relative to each other along the way to evaluate CLO/LOFT/OZ per 10 degrees.

More a plea from me and nothing against your effort or knowledge- But is there a BPL expert or friendly Pro who could weigh in too? Jerry is fighting the good fight, but my skull is thickening by the hour, lol.

The way they test down is to dry it, then put it in a cylinder of some size, then put a specific weight on top and let it compress the down that much

volume of cylinder occupied / weight of down is the fill power

assuming the specific weight is chosen to be similar to the pressure applied by the fabric in a sleeping bag, then this should be close to the actual volume occupied in a sleeping bag

so, 900 fill down will fill a little more volume than 850 fill in actual use

maybe higher fill power, since there are fewer fibers per volume has a lower clo per inch

I don't think there are definitive answers to all this