A CLO question: Is it possible to estimate?

Follow-up question about CLO:

Anyone aware of a table that associates CLO values with ambient temperatures? Yes, there would be a lot of variability in such a table (man, woman, age, wind) — believe me, I "get" the variability issue. But I'm looking for ranges, not point estimates. In other words, I'm OK with "just getting close."

For example, in another BPL thread one poster said something to the effect that a particular jacket had a CLO of 3.5, and that should easily take you into the 20 F range with only a light baselayer underneath. That is really helpful information, and I would love to be able to add the CLO numbers of my gear and get at least a rough estimate of how cold I can tolerate.

Also curious if the relationship between CLO and ambient temperature is linear, or perhaps logarithmic. I can imagine the required CLO numbers piling up quickly as you get into "really cold" territory.

Richard's plot:
http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

It's linear. Skin temperature when you're somewhat cold is about 92 F. Difference between the minimum temperature and 92 F is proportional to clo. If you have twice as much clo, you can do twice as much temperature difference.

You can guesstimate but just realize "CLO" is loosely defined around the average male with average metabolism, so really you'll have to do a lot of calibration for your own circumstances.

Clo is also relatively linear. I add the caveat though that below freezing there is a different linear relationship with a lower slope. I haven't tested this but the conjecture is based on phase change physics. Once the temp is below freezing the environment is not just trying to make your body hyopthermic, but actually trying to solidify your 70% of water by sapping heat. Therefore our bodies have to work harder in sub freezing temps. You'll notice that sleeping bag companies and MYOG wisdom also tend to subscribe to a similar philosophy when it comes to loft and temp ratings. Basically below freezing requires more loft to drop the temp rating 10F than above freezing (very roughly 1"=10F above freezing and 1.5"=10F below freezing).

Next to Richard N. I think I've done the most academic analysis of clo and insulation. I'll impart some of my wisdom…it's a fool's errand. First each individual's metabolism is wildly variable, both from person to person as well as from minute to minute depending on food, hydration, and health. Secondly the design of a garment can impart as much warmth as the insulation. Using stiffer outer fabrics that are wind proof vs wispy nylon that deflects in the gentlest breeze matters. Making sure hems, cuffs, and hoods are snug fitting is important.

Clo is a useful tool to compare relative warmth of jackets, but I find this is almost equally approximated by just looking at the down fill weight (heck even overall weight of a garment can be indicative a lot of times). It's akin to MVTR and waterproof ratings of jackets or denier of a fabric. It's fun, but try not to get too sucked into the details of the spreadsheets.

> I'll impart some of my wisdom…it's a fool's errand.

I hear you. There are variables to nail down all over the place.

All I'm looking for is a rough estimate of what CLO my bag is, and a rough idea of how far I might be able to push it by adding a down jacket. I realize I may be off by quite a few degrees.

I was able to roughly calculate my quilt's CLO based on Richard's statement:

"The most practical way for a backpacker to determine the dry Iclu clo value for an ensemble is to measure the thickness of each garment component; multiply the thickness by 4 clo; and then multiply by the percentage of an average body it covers."

Not entirely straightforward, as I had to guesstimate how much of the body the quilt covers, and then how much the pad (of different loft) covers. I think a quilt may loft over about 46% of the body. It does not cover the head (9% surface area) and the pad covers the back (figuring 49.5% as it includes back of the head). If someone has better numbers here, please chime in. These #s are from "total body surface area" from wikipedia, and they don't take into account that a quilt covers the sides of the body. So the quilt coverage would be underestimated.

But, using the figures above, a 2" lofting quilt (30 degree) would be 2 x 4 x .46 = 3.68. My pad would be 1.5 x 4 x .5 = 3. Add the two and you get about 6.7, which according to Richard Nisley's chart, would get you to … about 30 degrees (or a little less) sleeping temp … for a quilt advertised at 30 degrees. Coincidence? Or good model for establishing CLO?