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 Michael Martin (MikeMartin) - BPL Staff - MLife Locale: North Idaho Re: question for Richard... on 10/13/2008 22:54:53 MDT >> if you decrease the thickness of your typical UL sleeping bag by a factor of 2, you will not affect the warmth of the bag. Why? Because the density will be doubled, and so the clo/inch will double, but the thickness will be halved... so 2*0.5=1 and the warmth of the bag will stay the same.>> Spot on!Hmmm...I must be missing something here. The numbers aren't adding up for me.If you start with down at 2.16 kg/m^3 and 2.556 clo/inch, and compress it to 18 kg/m^3 at the end of the linear region, it would need a 21.3 clo/inch value (at 18kg/m^3) to have the same clo it started with.21.3 clo/in far exceeds even the maximum value of 6.562 clo/in which occurs well outside of the linear range.What am I missing? Edited by MikeMartin on 10/13/2008 22:56:55 MDT.
 Ashley Brown (ashleyb) - F Re: Re: question for Richard... on 10/13/2008 23:17:42 MDT Good question Mike! It would appear that the linear region would have to tail off rapidly at about 5kg/m3 in order to not exceed 6.56 clo/in at 18kg/m3.That would mean you could compress your bag by roughly 2.5 times before it started to become a problem.I note that in Richard's example figures for an overstuffed mummy bag the amount of down in the bag is effectively doubled during the experiment whilst still retaining a linear increase in clo... so equally well you can can be fairly sure that squashing a bag by less than 50% won't affect it's performance. Edited by ashleyb on 10/14/2008 00:39:51 MDT.
 Roger Caffin (rcaffin) - BPL Staff - MLife Locale: Wollemi & Kosciusko NPs, Europe Re: Re: question for Richard... on 10/13/2008 23:35:10 MDT And if you decrease the thickness of the down by a factor of 100 you will increase the density by 100, meaning that a layer of down one thou of an inch thick will have an insulating value *per inch* exceeding anything on the planet.Yeah, right. Beware extrapolations! Looking closely at what Richard wrote we find that the linear region only goes so far, then it fails. Yup.The insulating value of the down will rise with density for a little while, until the ends of the down fibres are starting to touch everywhere. When that happens the Kozeny equation (I think that's the correct spelling) breaks down, because it is mainly the air around the tips of the down fibres that insulates. Continuous filament insulation (synthetic) is not as good as down precisely because it does not have the fibre ends, only continuous filaments, to trap the air.The same thing explains why damp down is a poor insulator: the microscopic fibres start to stick together. Loss of ends => loss of trapped air => loss of insulation.Cheers Edited by rcaffin on 10/13/2008 23:40:36 MDT.
 Ashley Brown (ashleyb) - F Re: Re: Re: question for Richard... on 10/14/2008 00:46:17 MDT > Yeah, right. Beware extrapolations! Looking closely at what Richard wrote we find that the linear region only goes so far, then it fails. Yup.I don't think anyone is in disagreement on that point! The interesting thing from Richard's data however is that there *is* a significant linear region and you don't have to extrapolate beyond the data points to show that 50% down compression on most UL bags should not be a problem. Losing loft because your bag is damp is another matter altogether!
 Tad Englund (bestbuilder) - F - MLife Locale: Pacific Northwest Re: Re: Re: question for Richard... on 10/14/2008 09:29:46 MDT Richard, it has been too long since I was in school and I think I went skiing the week/semester they discussed thermodynamics. Maybe it’s too early in the morning for me but what is clo (I probable know this but I’m having a brian cramp). I think I’m following what you are saying but the clo thing keeps me guessing.I really appreciate you guys- It is not enough for me to just know I was cold but the why and how to fix it. It also helps in other areas to understand how not to let it happen with other equipment.
 Michael Martin (MikeMartin) - BPL Staff - MLife Locale: North Idaho Re: question for Richard... on 10/14/2008 09:46:20 MDT >> The interesting thing from Richard's data however is that there *is* a significant linear region and you don't have to extrapolate...Indeed. We're all on the same page here. My original point was that according to Richard's numbers, the linear region extended out to 18kg/m^3 and "flat-ish" region extended from there to 75kg/m^3. So my last example was actually interpolating within the values Richard gave us, not extrapolating past the data points.I suspect that the reason for the discrepancy is that the Y intercept of the clo/in vs density graph is above zero. If true, this would reconcile the data points we have been given. But, it also would mean that doubling the density would *not* double the clo/in -- even in the linear region.EDIT: I just found this old post from RN that supports my suspicion:http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/12505/index.html?skip_to_post=94791#94791(Look at the thermal conductivity vs density graph.)Cheers,-Mike Edited by MikeMartin on 10/14/2008 22:25:19 MDT.
 Richard Nisley (richard295) - M Locale: San Francisco Bay Area Re: Re: Re: Re: question for Richard... on 10/14/2008 09:57:32 MDT Tad,As a builder you understand that R Value measures the resistance to heat flowing through an item. clo is the same thing as R Value. To convert R Value to clo, multiply the R Value by 1.13931529284938. To convert clo to R Value, multiply the clo by 0.8832059100018.clo is generally easier for people to relate to when evaluating clothing or sleeping bags. 1 clo is the COMBINED insulation provided by a complete winter weight business suit ensemble. This ensemble includes the shoes, socks, underwear, shirt, tie, long sleeve shirt, winter weight pants, and winter weight jacket. Edited by richard295 on 10/14/2008 09:58:23 MDT.
 Tad Englund (bestbuilder) - F - MLife Locale: Pacific Northwest Re: Re: Re: Re: Re: question for Richard... on 10/14/2008 10:45:23 MDT Richard, Thanks- BTW is that a "Hickey Freeman" wool suit or a "Men's warehouse" wool suit? There is a difference. Just kidding.What does the initials "clo" stand for?
 Ashley Brown (ashleyb) - F Re: Re: question for Richard... on 10/14/2008 21:30:39 MDT Mike, I see what you are getting at and am now rather puzzled! Reading the thread you linked to I found some comments by Richard similar to the point I was making above:"You can increase the aerial density of 800 fill down about 2.5x before it is becomes less thermally efficient than fully lofted down. A compression sack will easily compress the down much more than this; so, it is important to let it loft up. This same phenomenon applies to an earlier thread dealing with the diamond quilting on a MB women's down jacket resulting in less loft than the rectangular quilting in the same man's jacket. Again, it doesn't make any difference."Further down the page..."If your Parmo raincoat doesn’t compress your Gilnet jacket such that the density increases more than 2.5 X, you should be fine. You can probably find hundreds, if not thousands, of Internet posts which make the statement that the loft of a down garment or bag determines its warmth. My contention is that this is true only if they are using the same fill power and density. You can make a down bag or clothing warmer by increasing its density even if the loft is less."I'm not quite sure how these statements can be reconciled with Mike's point that the linear equation seems to have a significant y-intercept constant (meaning that doubling the x value won't double the y value).
 Brad Groves (4quietwoods) - MLife Locale: Michigan Density: Warmth on 10/17/2008 09:56:51 MDT I'm a writer. My eyes (and mind) glaze over when I see equations. A couple of "real world" examples on density, FWIW. We all know and respect Western Mountaineering bags because, along with being light, they're really warm. If you've had the experience of comparing not just loft, but density of loft, of similarly rated bags, you know that the Western bags have more down in each baffle. In my shop right now I have about 40 models of down sleeping bags hanging. If I compare the density of loft between models, Western bags basically always win. The down vest I recently made used much more down than some would expect; several people felt it was overfilled. But it didn't lose any warmth. In fact, it's the warmest garment I have.To be as unprecise and speculative as possible, I'll also ask this: just how much loft does a goose have? The birds I've seen aren't several inches thick of loosely packed downy poofs. The down on the birds I've seen is pretty darn dense. Yet it seems to keep them warm...
 Kathleen B (rosierabbit) - M Locale: Pacific Northwest Goose loft on 10/17/2008 10:48:37 MDT Maybe those webbed feet are good ground insulation? Windproof outer feathers?I know of a PCT thru-hiker who used a WM Ultralite and was very cold on the last stretch of her trip. So she's thinking of replacing her bag with another brand. I would like to see her try better ground insulation. Just one 3/4 length closed cell foam pad, which probably smooshed over 5 months, probably had a lot to do with her being cold. Plus, like the first poster, she may have been wearing too much in too confined a space, actually being counterproductive with efforts to be warm. This has been an interesting thread. As I sift through the information I see the basic things to do are avoid tight or sweaty clothing, use effective ground insulation, and pay attention to where you sleep (under trees v. open, windy areas).Personally, I've found putting quality closed cell foam (gossamergear) over my Prolite 3 insulates me from both the cold ground and any cold air coming from the Prolite and I am much warmer in the same conditions than when I had the foam and Prolite reversed.