Quote Originally Posted by Just Bill View Post
Tulle (spell check got you, lol) probably isn't that much crappier than netting... so your test maybe more relevant than you think perhaps. Guess it depends if it's woven or fused a bit.
Solid fabric is probably better regardless.
I agree that tulle isn't necessarily bad quality, the Walmart stuff was just really bottom of the barrel. The test is definitely relevant though, I expect the noseeum to behave more or less the same, just not as extreme.

And if'n budget is an issue I strongly suggest you do a sample. This is all well and good to a point but wouldn't be the first Nisley, Jerry Adams, or other wonder theory that fell apart in real life. I still have a Jerry Adams inspired baffle quilt laying around someplace. All good folks with good ideas that inform the discussion but Mountain Hardware still more or less builds their sleeping gear the same way they have for decades for a reason.
Many of us do a 'pillow' say 20"by 30" we can test out an idea on. Gets you a little scale but not a big $$$ commitment.
That is good advice, and definitely the sensible course of action. Unfortunately, I am not all that sensible

When you chain the baffles together- this affects them too. Heavier fabric like 1 ounce may alter things... as does checking out something laying on a table vs hanging in space.
Karo step works pretty well in top quilts at mid range volumes around 2".... much less so at 3" and way less so as an UQ. Same theory, same math, same idea... but different applications.
Yeah, this sort of thing is what I've been trying to model in my research on under quilts. Unlike top quilts, the forces on under quilts are pretty predictable, and I have a hunch that I can use them to my advantage to create a more rectangular baffle. This is another idea that requires physical testing though. As the models can only get you so far.

As far as CLO breaking down...
I'm still a carpenter. Not even a tinknocker so I can't supply you with a paper or run you a number string.

I can point out one very simple real world application- Take my Neo-air Xtherm mat which is the gold standard of winter mats with thousands of people reporting warm nights at zero degrees easily.
Other than one fella here with one night reported... they don't work much past freezing in the air. Now you and I can convert with 1 CLO= .88R all day long and discuss the specs and insulating properties... but the simple fact is that the pad wasn't designed for convection losses and once it goes up in the air it's simply not as effective as it is on the ground.

While a bit simplistic- R value of a pad based upon air chambers and mylar simply isn't the same R value as its closed cell foam equivalent. Nor are any of the laboratory tests performed on anything higher than cot in a closed room or a slab with no airflow. It's just not an application that applies.

One could say the same for down as well. As far as I know... nobody has studied how down works when it's under you.
Above you... heat rises. Sides... more or less covered.
Below you... now what?
Gravity pulls the down to your body when on top. In theory you have increased density fill right next to you and low density fill farther way at maximum loft. This would put the best insulation right at the heat source.
A good bit of 'cold butt syndrome" is also the simple fact that cold air falls and can easily pool within your underquilt.
If the quilt fits poorly- your butt crushes out the insulation. If the quilt fits well- but not perfect- it's easy to get a small boundary layer of air to form or even the hot air rising out any leaks to cause cold air to be drawn in.

The specific reason the CLO breaks down though I don't have the science to express but likely you follow along.

There is a point of thermal equilibrium in all these insulation scenarios. As it gets colder- the difference between the 'inside' and 'outside' is greater.
CLO specifically wasn't really meant for applications outside building science as far as I understand... but was adopted and used at some point.

Point being...
We only throw off so much heat. (Watts)
Around 50*... we are tossing enough watts out so that the outside surface of our sleeping gear is still (more or less) equal to or above the outside air temp.


I toss 70*... it's 50* out... the surface of my summer quilt is probably around 50* (or close enough).
The point of thermal equilibrium is at the edge of or outside our sleep system.

I toss 70*... it's zero out... the surface of my winter quilt is probably around zero degrees... maybe 10*.
The point of thermal equilibrium is within our sleep system.

Or perhaps my science terms are a bit scrambled and I should be saying thermal gradient... regardless I'll push on.

So how much loft do you actually have? Do you have 4" of down in your zero degree quilt? Or do you have 3" of down you can heat... and 1" outside the reach of the watts of your personal output?

I always explain sleep gear like a lightbulb. (as that's basically how the calculation works anyway with W and surface area/mass dictating heat output of the sleeper.)

If you are a light bulb and you put out 40W or so... you can only light up a room 8'x8'.
If you are a hot sleeper you might put out 60W... you can light up a 10'x10' room.

But put either of you into a 12'x12' room... and there are some dark corners your bulb cannot reach. Your bulb is only so bright... and it's on a dimmer switch set to turn down by about 20w when you fall asleep and you metabolism drops off.

This is the reason the CLO formula breaks down.
It is a linear formula for a non-lineal equation... or perhaps a 'capped' equation is a better term.

Watts is a fixed number for us in the outdoors unlike the other numbers it is not infinite. It is why most old woodsman here can tell you that 2am fire tending, hot water bottles, midnight snacks, pre-bed jumping jacks, chemical packs or a dozen other little tricks are needed in deep cold. The only way to push that heat into the dark corners is to ramp up your metabolism just before bed. To increase your watts, supplement the old heater.

Otherwise increasing CLO/Loft/R-value only makes the dark room bigger and bigger. It's wasted space since your light simply cannot reach it. Sure it may cut down convection loss... but at some point if you are not pushing out enough heat... there is nothing left to conduct through that insulation as it is outside your 'range'. Insulation only traps the air we warm so if we never warm it... might as well not be there at all.

If you can 'go to bed hot' or supplement your warmth... then you can turn up the bulb and illuminate more of the darkness. Only then that insulation can be used to hold that heat longer.

The limiting factor in the CLO formula is us... watts. Generally speaking 40-60w is about as bright as we get when laying down. I'm sure you can look up your own met chart of choice but 80 at rest but fully awake rings a bell as a maximum realistic number.

I am unclear why this isn't talked about... other than the fact its a fairly limited subset of an already limited application in overall insulation science. Arseholes who camp in subzero temps are not that high on anyone's radar... even for military application it's a very small subset. But nearly any of us who do camp in deep cold understand this limitation pretty intimately.

This is also why limiting yourself to three season temps of 20-40*F is also more valuable... because you don't have to deal with this issue as badly.
While 40 is not 40.... zero is zero. There is much less ambiguity when we reach zero degrees than at higher temps.

There is actual truth to the term 'experienced sleeper'... what happens to those who acclimate is that their metabolism doesn't kick down that 20W or so most of us habituated folks do when we fall asleep.
It's also one reason when you may read an 'Artic gear' study for military use you can pretty well discount it for Joe Average coming from his house to a Frozen Butt hang for the weekend.
That is one of the flaws in the EN testing and some of the US military tests that run numbers based upon fit healthy mid twenties males who are 'experienced' sleepers... They are literally the brightest bulbs in the bunch! That same military member 10 years older may have lost 10W of output as his metabolism slows. It would drop another 10W if he stopped being active and put on a few pounds once he got assigned to desk duty.

However that is another subject for another day...
Okay, I see what you are talking about it now. I was a little confused by what you meant by "break down", as I didn't think of it quite the same way, but I know exactly what you mean.

There are three different factors that you are talking about here: one is how the insulating material changes at low temperatures, two is how other factors (like convection and radiation) become more important at low temperatures, and the last one is how humans change at low temperatures.

I actually have a good amount of experience with building science, as it is a hobby of mine (I have really weird hobbies), so I have a good grasp on the former. The r-value of most materials varies with temperature. This article over at GreenBuildingAdvisor explains it well. In general, most insulation actually performs better at cold temperatures, meaning a fiberglass batt rated at R-13 at 72 degrees might be closer to R-14 at 0 degrees. This tends to be especially true for natural materials, like down and wool: after all, the goal of the animals is to not freeze to death in the cold, but also not to overheat when it is hot either, so these materials evolved to insulate better when it is cold than when it is warm. However, materials made of foam are different: they usually have trapped blowing agents, which can condense at low temperatures, reducing thermal performance. Polyiso is a great example of this, it can go from more than R6/inch in hot weather to less than R5/inch in cold weather. Closed cell foam sleeping pads have the potential to behave similarly, but it probably won't be as extreme.

And as you correctly point out, anything placed in the air is liable to have higher convection and radiation losses than on the ground. Neither of those are accounted for in R-value, which purely measures conductive losses. Beyond even those concrete measures, the difference between a top and bottom quilt, as you suggest, are important. For example, a top quilt will likely have more convection to deal with, whereas a bottom quilt is more vulnerable to wind-washing. Both can have a big effect on the comfort of the user, and would not be accounted for by a simple R-value measurement. Plus when you are sleeping on the ground, you gradually warm the ground up beneath you. No such luck with air.

All that goes to show that relying on simple R-values or CLO values is foolish, especially as the temperature grows more extreme. And that is before you throw in all the human variation stuff that you mention. Some things certainly require experience to judge correctly. That's why these quilts are rated by temperature, and not by R-value, and the reason that center of baffle height is a better proxy for temperature rating than trying to turn the R values into something meaningful. All the R-values are really useful for is comparing baffles to each other — an R6.5 baffle will be warmer than an R6.2 baffle, though whether either are warm enough depends on many other factors.

As a side note on the thermal gradient stuff, it is actually an important point. I have been using the free 2D modeling software THERM from the Lawrence Berkeley National Laboratory to try and gauge the comfort of different baffle shapes and thicknesses. Since it was made for construction purposes, I have to input custom materials for it, but it does a wonderful job of displaying the thermal gradient within the baffles. It doesn't provide very much information that could not be interpreted from R-value, but seeing it is still helpful. Plus it handles radiation losses easily.