Thermawrap warm enough?

Doug,

Good question – I personally think your Thermawrap with your Micropuff vest would be warm enough.

I’m also interested in some experienced-based opinions regarding your question. I am planning for a trip in mid-September to Rocky Mountain National Park with similar temperatures to what you’ll see.

Averages: Low 30’s High 50’s
Records: Low 20’s High 70’s

My tentative layering system is similar to yours:
Base layer:
– Patagonia capilene II long sleeve shirt (5.9 oz)
– Patagonia capilene III long underwear (6.9 oz)
Mid layer:
– Merino wool long sleeve 1/4 zip sweater (11.3 oz)
High loft insulation:
– Patagonia Micropuff jacket (11 oz)
Outer layer for rain:
– Patagonia Rain Shadow jacket (13.8)
– GoLite Reed pants (5.9 oz)
Outer layer for wind:
– GoLite Ether (3.2 oz) wind shirt
– If needed i'll use the above GoLite Reed on my legs
Total weight of above: 58 oz (3.6#)

Sleeping bag:
Montbell UL SS 800 fill down #3 (30 degree bag)

Some other clothing accessories:
– Cloudveil glove liner (0.85 oz)
– Patagonia Fingerless gloves (2.2 oz)
– MLD eVENT rain mitts (0.95 oz, need to purchase or find alternative)
– Smartwool lightweight balaclava (1.65 oz)
– S2S mosquito headnet (1.2 oz, not sure if bugs will be an issue)
– ID eVENT gaiters (2.3 oz)

I think a question we’d both be interested asking is if we need the mid layer (your Marmot Reactor fleece zip and my merino wool 1/4 zip L/S sweater)? Perhaps they’d be useful when hiking and your Thermawrap (and my Micropuff) would be to hot and our long underwear base layer would be too cool. Though, I could toss on my GoLite Ether over the capilene. Leaving them home would save us both almost a 3/4 of a pound!

In a related thread Brett1234 stated the following: “IME, Thermawrap is good to 0C while active with a wool-1 base.” I’m assuming by “wool-1 base” he is referring to a lightweight merino wool shirt.

See: http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/8910/index.html

Brian

For me, a synthetic tee and a MB Thermawrap will keep me warm down to 45F when at rest — or 40F when adding a shell layer. I know I would want something more than just the Thermawrap at 32F / 0C (yes, I live in sunny southern Cal).

My MB Down Hugger No. 3 bag keeps me warm to 30F. Much below that, I start feeling cold. I haven't actually done it, but I believe I can take the bag down to 20F if I wear my Thermawrap top and bottom.

Ben, Do you think the addition of his micropuff vest (over the Thermawrap) would keep him sufficiently warm for said temps? Or would your arms get to cold? I have not heard much about his bag and if the rating is spot on. Your comments regarding the montbell #3 bag seem consistent with others.

Regarding lower insulation: I assume long underwear (under nylon pants) is sufficient for these temps when active. However, do you think thermawrap bottoms would be a more versatile choice as they’d be the choice for in camp/sleeping?

Hi Brian:

Here are my thoughts/questions reading Doug's post above:

1. Has he used the Marmot Hydrogen at or below its rated temp? Is it accurately rated to 30F for him?

2. If (1) is affirmative, then I am thinking that the addition of a Thermawrap is good enough for a 10F boost, and adding a rain jacket on top should be good for another 5F boost — or 15F in total. That should take care of his upper body. He may wish to bring a vest or fleece for "insurance" — but I don't think he needs both vest and fleece in addition to the Thermawrap.

3. But what about the lower body? Long underwear and rain pants may not be enough if temps drop to 20F. And if the Marmot isn't accurately rated to begin with, then his legs may really feel the cold. Doug might want to swap one of his top insulation layers for a bottom???

I have the thermawrap jacket, 2006 model, and I use a 32-degree rated bag (WM Summerlite) and in the conditions described in the original post I'd be confident that setup would work for me. But sort of like someone recommending a particular pair of shoes, YMMV a lot. It depends on how your body handles cold in general, how in-shape you are, what you're eating, how active you are when on the trip, whether you tend to sleep warm or cold, etc etc.

I think the only way to really know how well you'll do with a gear/clothing setup is to have some experience at something sufficiently similar to calibrate it to your own body. If not, I'd go a bit conservative, i.e., risk carrying more (layerable) clothing than you might need until you've been able to get that direct experience.

I have used the Marmot Hydrogen bag one night down to 26 or 28 degrees, wore the Thermowrap jacket and was warm enough. Seems like adding full thermal underwear, tops and bottoms, I'd be happy down to 20 anyway, maybe cooler with the vest and a fleece cap.

I'm figuring to wear the Reactor while we're hiking, since it will breath much better than the Thermowrap, then add the Thermowrap and/or vest at rest stops and in camp.

I'm not so sure about hanging around camp with the Thermowrap, vest, sweater and longjohns if it gets really cold. I'm strongly tempted to try it, though. I think I was happy on the last trip wearing the Thermowrap, vest and a cap the evening before the 28-degree low. I'm curious if anyone else has experience with similar gear and temps.

I guess it won't get really cold this trip unless the weather is clear, in which case at least I should be dry. With nine days food (20 lb) and the light gear mentioned, my pack is still looking like 48 or 50 pounds. See my profile for tentative gear list (Comments, critique welcome). It's 10 or 12 pounds lighter than a six-day trip I took last year.

Has anyone every used this product for water treatment??? I am wondering about the flavor and the efficacy.

thanks,
Jason

Jason's post above reads like a pretty blatant — and lame — attempt at free advertising.

Wouldn't waste my money on it Jason.

what do you want to bet that was a post because of the comments of 'clothing supplements' above?

I built a thermal model for Doug Loshbaugh's proposed Brooks Range Trip. In summary it showed the following salient points:

-Neither the long underwear nor the Marmot Reactor Zip Fleece is required for the worst case low temperature scenarios. Eliminating these two items will save approximately 2 lbs.
-My thermal database lists Exceloft at .040 W/m K. My intuition is that it should test closer to .033 W/m K if I went to the trouble to formally test it. .033 W/m K would put it about the same clo/oz as the latest Climashield XP or Primaloft One. I did the calculations using both Exceloft values and discovered there was only a 1.1 F difference between whether this insulation tested at the top of the pack or in the middle. I used the more conservative worst case (WC) values for all insulation requirement calculations.
-Recommended clothing combinations for camp chores, hiking, and sleeping are listed in the model. The items in yellow are proposed solutions and all other values are used to determine the requirements.

Thanks for the calculations!

What the…?!?

Richard,

It'd be sweet if you could actually do a full write up of whatever it is you did… how you came up with values, etc. That appears to be a beautiful piece of work that you've done….

Joshua – It is a big unknown to me what percentage of the forum readers, besides the person requesting information, are interested in the same question. Also unknown is what level of detail is appropriate to answer a question. I believe that it is generally prudent to avoid the situation known as, " I just wanted to know the time, not how your watch works."

People are comfortable when the same amount of heat generated is the amount lost. Your body is similar to an automobile in that 75% of the energy used results in heat and only about 25% in useful work. We need to know the activity level in order to calculate how much insulation is required for a specific temperature. The base metabolic rate (1 MET) is the amount of energy you are burning when laying down resting but awake. When asleep you generate about .8 this amount (.8 MET), doing camp chores twice this amount (2.5 MET) and backpacking an average of about seven times this amount (7 MET).

As an ultralight backpacker, you want to select, from your inventory, the lightest combination of insulation that will insure comfort for all activities within the estimated temperature extremes. You first determine how much insulation you need to sleep comfortably at some specified minimum temperature. In Doug's case, he was planning on using a bag that had been tested using the EN13537 procedure. I believe this is the most accurate testing system available. His Marmot Hydrogen's 30F EN13537 Lower Comfort rating means that it averages 5.88 clo. The insulation required for a temperature rating can be found on page 32 in EN13537 Convert m2 K/W insulation values to clo values by dividing by .155.

The BPL reviews on most clothing items give the insulation weight in oz/yd2. The clo/oz ratings for the most common backpacking used insulations are:

Cotton .04 clo/oz
Merino wool .08 clo/oz
Polartec 100,200, and 300 series .16 clo/oz
Polarguard 3D, .63 clo/oz
Exceloft .68 clo/oz
Polarguard Delta, .68 clo/oz.
Climashield HL, .68 clo/oz.
Down (550 fill) .70
Primaloft Sport, .74 clo/oz.
Climashield Combat, .79 clo/oz.
Climashield XP, .82 clo/oz.
Primaloft One, .84 clo/oz.
Down (850+ fill) 2.53 clo/oz

Multiply the insulation weight in oz/yd2 times the clo/oz to determine the Item clo value. This tells you how warm it would be if it covered your complete body. You then need to multiply this number by the % of the body is covered by the item to calculate the clo Iclu value. The clo Iclu value allows you to determine the effective insulation by combining items with different insulation values. The average vest covers 36% and the average jacket covers 48% of your total body area. These % adjustments were made to the appropriate clothing items. After adding all of the clo Iclu values, convert this number back to m2K/W by multiply by .155. Then look at the above referenced graph to determine what temperature that combination yields for comfortable sleep.

For activities other than sleep, you generate more heat and so your insulation needs are reduced in proportion to your MET level. If we wanted comfortable sleep at 40F, we can see from the above referenced chart that the insulation required would be approximately .76 m2K/W. We divide by ~.155 to find the equivalent clo value of 4.84. We then need to divide this by increased heat generated from camp activities or 2.5/0.8 which yields the required insulation of 1.55 Iclu clo that is shown in the chart. The clothing combination that is most appropriate for this scenario is determined by combining items to find the closest clo Iclu total. In this case it happened to be our base clothing + Patagonia Micro Puff + Montbell Thermawrap + rain gear yielding 1.95 clo Iclu.

The information about how good the proprietary Exceloft insulation is illustrates an important point: to keep things simple, just focus on the thickness of the combined insulation layers.

EN13537 should provide a hot link entitled EN13537. Until BPL fixes this bug you will have to manually place the URL http://www.mammut.ch/mammut/uploadedFiles/Sleep%20Well_Pt1_E.pdf#search=%22%22A%20Review%20of%20Temperature%20Standards%22%22 in your browser.

Richard, in my case you definitely did not run into "what time is it?" that kind of information is exactly what I was looking for.

Of course, it takes a while to digest it. That study of "EN 13537" doesn't have any notes on mats beyond 'use a good mat'. I presume that this all goes to heck if one is not used (is there a similar procedure for deciding how much 'mat' one needs)?

Question, when (in your explanation) you mentioned a graph, I suppose it's the m2/K / temp comfort one in the study PDF?

Question 2, you mentioned keying in on thickness, I'm not sure I quite understood what you meant. I'm having a hard time figuring out how, exactly, that worked into your system / spreadsheet.

Actually, if you wouldn't mind emailing me your spread sheet, I'd love to have a look at the base calcs / process.

Josuha – The EN 13537 tests are done with the old orange 1.75" Thermarest standard. Its specs are R value = 5.8 or M2KV = .876. Last year I posted a very detailed explanation of how to adjust sleeping bag ratings for different pad insulation values and sleeping positions. The series of posts were in response to questions Bill F had regarding quilts design.

The graph is on page 32 of the URL link I provided in my latest post calling out the long outstanding BPL forum bug.

By keying in on thickness, I meant that for most purposes, you only need to measure the thickness of the insulation with a ruler to gauge its relative contribution rather than making things more complex by factoring in the insulation type. In general, something twice as thick will have twice the insulation value. The relatively thin .234 thickness of the Thermawrap has a relatively small impact by increasing a sleeping bag rating 6.2 F.

For most of my trips I just calculate what I need in my head using a very simple approach. It should be clear why this works by going through the detailed approach one time.
-For sleeping, 20F requires approximately 2 inches on insulation. Add 1/2 my jacket and (or) vest thickness total to my sleeping bag total to find the miniumum comfort temp
-For sleeping, every 1/2" difference in insulation changes the rating approximately 20F
-For camp chores wear, I just divide the sleeping bag insulation amount I would need for that temp by 3 (2.5 MET/.8 MET = 3.125)

Joshua: "What the…?!?"
LOL..
I had the same reaction seeing my first R.N. 'clo' post. Its these sort of nuggets that I copy and save, which keep a gear geek like me coming back to BPL for more.

The simplified approach in Richard's last post is his rule of thumb which I have been using with success for a year now. A key piece of information is knowing your own metabolic rate, which introduces a scaling factor into the clo results (linear or not, Richard?). For example a girl I hike with has to use a factor of 2; twice the insulation I would use to stay comfortable. But, true to the model it is predictable, so she can plan what to carry and nothing more.

Brett – You are correct. I made a detailed series of posts about this phenomenon in the forum a while back. In addition, those posts contained a BMR calculator URL. Age, sex, weight, and height are inputs to calculating a BMR.

The function is non-linear. Below is what just the age and sex elements look like graphed. The arrows point to the typical BMR age and sex values used in the calculation of sleeping bag warmth standards for either a male or female.

Richard, thanks for that chart. I saved it as well.
What about fat% (insulation) in the BMR calculation? My GF gets cold easily, as well as having a lower BMR. I suspect it is because she has low fat content and thus looses the metabolic heat faster than a well insulated person would.

Can you integrate a term or coefficient for body fat% into the currrent four term forumula (Age, sex, weight, and height) and re-post a new formula?
Or how about ignoring it for BMR and calculating it as insulation? Maybe use the R value of human fat, convert to clo, multiply by average thickness and % coverage, and add it into the existing clothing summary as a literal Base Layer?! bizarre but probably accurate to a first order approximation.

Brett – Use the more comprehensive calculator set at http://home.fuse.net/clymer/bmi/ to determine both you and your girfriend's Harris and Benedict BMR plus all other possible correlation factors. Waist size is the only additional input parameter.

Richard, thanks for that link. I calculated our BMRs, but the waist size is not used in the BMR calculation. I varied only it, and BMR did not change, only fat%.
I believe a higher fat content would trap the heat produced by the BMR (insulation), and a lack of it would allow higher heat transfer thus actually requiring a higher than text-book BMR. I dont know, there's more to this than I thought..
Time for some Google research.

Brett – The higher the muscle %, the higher the BMR. Generally this factor far outweighs the offsetting insulation value of more fat.

Richard,

I'm following everything just fine (multiple Heat Transfer and Thermo classes helps this make sense… though I am a bit rusty), however I'm having a hard time figuring out what the "average" BMR / surface area used in that report is. (note, I can figure out W / m2 of that BMI calculator just fine)

Also, once that is figured out… if a person has a BMR of 1.2 times the average… they will likely need approximately 20 % (the math's a little different than that, but that's easier to write) LESS thermal insulation (clo or m2K/W), in order to balance their heat production with their heat loss, correct?