Hi Everyone,

I’m contemplating layering a MB Down vest under a MB Down Parka for cold conditions. From my calculations it appears that this would be far better lclo-wise than the MB Alpine Light Jacket alone (or discontinued Alpine Jacket). For simplicity, I’m just focusing on the torso where the vest would provide coverage.

My proposed layers:
Silk weight Capilene: 0.19 lclo
+ MB Down Vest: 1.78
+ Air pocket #1: 0.8
+ MB UL Down Parka: 1.78
+ Air pocket #2: 0.8
+ Shell: 0
Total lclo: 5.16 (including air pockets) or 3.56 (not including air pockets)
This compares to 2.51 for MB Alpine Light Jacket and 3.77 for MB Alpine Jacket.

I’m skeptical of this calculation. Is this right or am I missing something? I would guess that (not counting the air pockets) the combo would be equivalent to the Alpine light for the Torso since the Alpine Light has twice the down… but it appears to be much better.

Reference posts by Richard Nisley:
lclo measurements: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=18950
Value of air pockets: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=13697

i think yr calculation are off ... 0.8 clo is basically a 200+wt fleece i believe ...

and the vest i dont think will have the same insulation as a parka

id look at the total amount of down personally in that combo

Edited by bearbreeder on 11/09/2011 09:25:38 MST.

"the combo would be equivalent to the Alpine light for the Torso"
They look right for the torso, but the vest doesn't cover the arms. You might need to include an analysis of the area covered, not just clo, to be completely accurate.

Eric -- see this post regarding the value of air gaps. Scroll down to Richard Nisley's table almost at the bottom. It claims iclo of .8 between an MB inner jacket and Cocoon Pro Parka. http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=13697

Walter -- I would guess they would be equivalent for the Torso based on the down, but in fact the layering strategy appears to result in a much better iclo than the Alpine light alone even if you discount air gaps. Yes, I can extend the analysis to the arms/hood but I want to make sure my logic is sound first.

Edited by tunaboy999 on 11/09/2011 09:38:20 MST.

rutherford ...

ill defer to mister nisley on the math ...

but i do own a MB exl and an EB downlight vest which i do use on combination on occasion and these together are roughly equivalent to yr proposed system .... i also own a westcomb kokanee which has an iclo of 3.22 .... and theres no way the combo of the exl and downlight vest feels "as warm" as the kokanee even without using the hood ...

what's the difference between clo and intrinsic clo?

intrinsic clo is clo normalized by surface area, so you can compare the insulation value of garments of different sizes (hats, gloves, vests, jackets)

clo is not dependent on area

it's the same clo value whether it's a bigger or smaller item

Jerry,

Rutherford Platt is correct. If you know the intrinsic clo for one garment, of a specified size, in a similar manufacture's series, you can estimate the clo value for all of the garments, of a specified size, in that series. For example, if you know the intrinsic clo of a MB UL jacket, you can approximate the clo value for the MB UL vest, jacket, and parka. They all cover a different % of your body surface area (BSA). The clo value will increase as the BSA covered increases.

The amount of down is increased about 7% for each size increase for down garments but the synthetic areal density stays the same for synthetic garments. So there is a slight calculation difference between down and synthetic mixes.

The simple thing to understand is that a parka will have a clo value about 7% more than a jacket. A vest will have a clo value about 25% less than a jacket. A down jacket in size large will have an intrinsic clo value about the same as a size medium jacket and a clo value approximately the same. A synthetic jacket in size large will have an intrinsic clo the same as a size medium jacket and a clo value which is slightly less.

Edited by richard295 on 11/09/2011 20:37:33 MST.

Richard -- do you have any thoughts on my original post?

Thanks Richard

So intrinsic clo = clo * body surface area?

So you could, for example, compare 2 jackets? If they had the same clo but one was longer it would have higher intrinsic clo so thus be warmer?

edit: okay, I just reread your post and that's what you said, I think I'm tracking you now : )

then the only thing is that I've always thought a thicker vest was warmer than a jacket. insulation around your torso provides more warmth than around your arms...

Edited by retiredjerry on 11/09/2011 21:05:53 MST.

Rutherford,

For these calculations I used a regression that I derived from actually measuring all of the MB product line. The regression evens out the readings and varies slightly from the actual measurements.

You should only add the boundary layer clo value one time (.6 -.8 clo) for a complete ensemble. This assumes that your layered garments are the same size and very small air gaps between them are offset by the compression of the under garment(s).

For approximation, a typical UL backpacker’s base layer ensemble is about 1 clo. By contrast the relevant ISO standard lists a typical winter base layer at 1.3 clo but, this includes a heavy sweater as part of the base ensemble.

The MB UL Down Vest has an Iclo of ~1.45 and a BSA of 36%; this provides an ~clo value of .522.

The MB UL Down Parka has an Iclo of ~1.92 and a BSA of 52%; this provides an ~clo value of .998.

If you are sheltered from the wind, you can include a boundary layer of .6 clo for a total of 1 + .522 + .998 + .6 = 3.12 clo. For the average male, doing camp chores, this will yield a thermo-neutral temperature of ~25F.

The MB Alpine Light, in place of the UL Vest and UL Parka would yield an Iclo of 2.70 and a camp chores thermo neutral temp of 30F (5F less than the UL combo).

The MB Alpine Down Jacket (now discontinued), in place of the UL Vest and UL Parka would yield an Iclo of 3.74 and a camp chores thermo neutral temp of 19F (6F more than the UL combo).

Richard,

Thanks so much -- that was very helpful. Just for clarification...

Can I factor in a boundary layer of 0.6 clo with any ensemble that includes base layers, insulating jacket, and windproof shell? Or does it require the layering of two insulation layers such as the UL vest and jacket?

Also, following up on Jerry's question, is there any validity to the idea that we should put more insulation on our core/head than around arms/legs in regular non-hypothermic situations?

RVP

Edited by tunaboy999 on 11/11/2011 17:49:00 MST.

Rutherford,

1) The boundary layer applies to any ensemble, if you are sheltered from the wind.

2) Jerry is correct as it relates to the benefits of a vest. This question is addressed by William F Forgey MD in his book, “Hypothermia”. He explains that the body’s vasoconstriction mechanism (to prevent heat loss) is activated much earlier and effectively from your body sensing your arms are cool. This results in the core temp not dropping as fast as it will with a jacket.

As it relates to head insulation versus the rest of the body, the additional insulation benefit occurs only after hypothermia has set it and shivering begins.

Thanks again Richard.

It's interesting that the Montbell UL Parka + Vest ensemble is ~15% warmer than the Alpine Light Jacket ensemble even though the amount of down is identical at 4 oz and the weight is nearly the same at ~13 oz.

RVP

If you're going to be even somewhat active with the vest/jacket combo the lighter insulation on your arms is actually just what you WANT to have. Insulating arms less than the torso is generally the best combo unless you are going to be totally sedentary.

In very cold weather when ski touring I have use both a fleece vest and a Polarguard filled vest over a base layer and heavy sweater. At 10 F. down to 0 F. I was just right, even after stopping for 15 minutes.

BTW, you can modify a jacket to have zip-off sleeves fo you always have the option to put them back on, say at camp. A few jackets come from the factory this way.

Edited by Danepacker on 11/12/2011 12:44:17 MST.