Torso Blanket

Theoretically your Torso blanket will cover about 18% of your body surface area. The 3 inches of incremental down torso loft coverage will provide approximately 19.7 clo *.18 = 3.5 clo of effective incremental insulation. If your existing sleeping ensemble is keeping you warm enough to sleep at 35F, the addition of this element will should keep you warm enough to about 0F (edited to replace -12F which was in error). Your special made item, effectively the equivalent of an expedition parka draped over a conventional sleep system, will work the same.

A theoretical of -12F in this case of only added torso insulation probably isn’t accurate. His toes will be icicles.

Yes, Yes,
Icicle toes wouldn’t be good.
The point to this is since the torso blanket is over the heart, (and vitals) then would the warm blood flow warm the rest of the body up to be able to with-stand another 10* temp drop?

Aaron wrote:
“Icicle toes wouldn’t be good”.

On the GA Hike I just got back from I made and used a pair of “Toe Cozy’s”. I made them out of a piece of the CS-Combat Bivy Liner I had left over. Hand sewn very simple and they worked great. I will post a few pictures when I get things sorted out later today. I have only been back home about an hour.

Just a few observations about the theoretical temperature rating of the torso blanket. First 0.1 clo increase generally represents 1 deg F increase which would only get the temp rating to 0 deg F, not -12. Next, most of the commerical sites I looked at rated down bags with 6in of double loft (3in single loft) at about 15 deg F, which would give them a clo of 5.5 not 19.7. Also, a quilt would be slightly less warm per inches of loft due to draft and loss of bottom insulation which does add something even though it is compressed. I’m assuming he would have his arms in the torso blanket, so the % body surface area covered would be 9% for the chest, (% for the back and 9% for each arm = 36%. I’m not sure if I should use both chest and back since one won’t be covered.

Anyway, the best increase would be 5.5 x 0.36 = 1.98 clo which would get you from 35 deg to 15 deg if you can keep your toes warm.

Well, that’s my 2 cents.

I have a Marmot Atom 40 degree bag which on its own is only good for me down to the mid 40s (I’m a cold sleeper, with my torso being the part that gets cold). I’ve started using my Western Mountaineering Flight Jacket as a torso quilt inside the bag and this has allowed me to sleep comfortably into the high 20s and tolerably down to the low 20s.

Graeme-Based on your real-world experience, I rechecked the theory and my back-of-the-envelope-calculations. Paraphrasing your post: “…comfort was increased from approximately 45F to approximately 25F with the addition of a WM Flight jacket.” The WM Flight jacket has 1.85″ single layer loft vs. the 3″ in the torso blanket post and the coverage area is different. None the less, your example is still extremely useful.

For the average male, a 45F minimum comfort level, with a 10mm foam pad, equates to approximately a 4.4 clo bag.

Your jacket covers approximately 48% of your body surface area. If you are a back sleeper, 65% of the 48% would not be compressed. This yields approximately 31.2% effective incremental body surface area insulation.

1.85 inches of the best 800+ fill goose down = 12.14 clo (I used this down’s insulation value in my original post). 1.85 inches of 550 fill down = 8.27 clo

800 fill: 12.14 * .312 = 3.79 effective body insulation clo. 550 fill: 8.27 * .312 = 2.58

Using the EN 13537 Comfort Limit calculations 800 fill would increase the value of your sleeping ensemble to approximately 8.19 clo and for 550 fill, 6.98 clo. The resultant combined temp rating value for 800 fill would be 6.1 F and for 550 fill would be 18.7 F.

My best guess is that WM is using close to 800 fill down but by using your jacket inside the sleeping bag it’s loft is being compressed and consequently yielding an insulation value close to uncompressed 550 fill. To test this theory get inside your bag without the jacket and have someone measure the distance from the top of the bag to the floor. Next put your jacket on, get inside the bag, roll around a couple of times like you would during your sleep, and then have someone repeat the measurement. If the top loft is not close to 1.85″ more I rest my case.

James-You got me! I apologize to you and poor Aaron, I could have frozen him… arrgh.

1. First 0.1 clo increase generally represents 1 deg F increase which would only get the temp rating to 0 deg F, not -12.

I used the most recent International standard on this subject, EN 13537 Lower Limit, for my posts. For an average male, 50F requires ~3.94 clo and 0F requires ~8.78 clo. 50 / (8.78 – 3.94) = .1033 F / .1 clo. We were in sync up to this point. I did a table lookup in my data using the total clo value of 8.8. My column for EN 13537 shows 0.56 F which matches your result. The number I erroneously posted first was from my adjacent column and was not valid. Sorry.

2. Next, most of the commercial sites I looked at rated down bags with 6in of double loft (3in single loft) at about 15 deg F, which would give them a clo of 5.5 not 19.7

The EN 13537 standard for a 15 F Lower Limit rated bag is 7.3 clo (1.13 m2K/W) FOR THE COMPLETE BAG… most American bag temp rating were created by marketing departments. 19.7 clo is for a small segment of the area being insulated. The resultant COMPLETE BAG insulation would be 8.72 clo. 8.72 clo yields a EN 13537 lower limit rating of 0F. Even a conventionally designed sleeping bag has dramatically different insulation values between the top and bottom layers because of body compression. Aaron just extended that asymmetry.

3. I’m not sure if I should use both chest and back since one won’t be covered.

The torso quilt will not add any insulation to the back and so 36% body coverage is not valid. What typically happens in border-line temperature situations is the person goes into a side fetus position to conserve warmth. This reduces the bottom insulation contribution from about 35% to 18% and increases the benefits of the top loft. A quilt is less likely to compress a torso blanket than a small sleeping bag would be. Also Aaron stated that he overstuffed the torso blanket which further reduces loft compression.

Considering we both had errors in our respective models they came out surprisingly close. My gut tells me that you are probably closer. Thanks again for your input.

Richard,
Because of your detailed post, I decided to get a little more detailed as well.
For the Torso Blanket I sewed the baffles by adding 3″ for each baffle plus 1″ for the edges. Sewing the baffles in half makes it 1 1/2″ and with each side sewn together it gives you about 2 1/2″. The loft is a good 3″ though. This is also an excellent and easy way to do baffling.

This gives you 2 fabric pieces 25″x 50″ or 2000ci. With .85 fabric this comes out to 1.311oz. To get 3″ of loft with 800 fill out of 23″x 27″ I need 2.295oz. Added together gives me 3.606 ounces.
So I guess I didn’t over-stuff it at all.
I may just have to go out and get down to 25*. I have socks that will take it. I just need to wait 2 months and make a 2 hour trip for it.
The main purpose of this piece of gear is actually to be included during next years JMT unsupported attempt. My layering as of now will include long sleeve rail riders eco-mesh shirt, patagonia r-1 flash, the torso blanket, dry-stopper rain gear, and a 40″x 96″ polycryo groundsheet to used as a tarp. I will also be laying on a torso length 1/4″ pad.
While sleeping from 8-11pm, or less, every day. In late August, I should only need to be able to keep warm down to 35-45*.
I will definitely be testing the torso blanket out with my quilt to see how much of a difference it will make in order to see what I can expect while on the trial.
This is the reason I am asking to see just how much it would help and if any one has used a torso blanket as an additive with their bag or quilt.

Richard,

Thanks for your insights on the temp rating. I didn’t even know the EN 13537 existed. Its not perfect but it sure beats the way most manufacturers report their bag ratings. Do you know where I can get the EN 13537 report for free? The ANSI website was trying to sell it for $169.

Not to beat a dead horse (I know clo has be discussed in other threads, but I was wondering why the clo value would be higher for a small area than for a full bag. It seems to me that if you just covered the torso of the maniquin it would take significanly more energy to keep it warm, dropping your clo.

Also, I guess I always assumed that per inch loft 800 fill and 550 fill down insulated the same. I figured the wieght advantage came because 800 lofted higher per oz. Does the 800 fill down just cut down on airmovent more or is there another reason for the difference?

Thanks,

James

James-Sorry, but I am not aware of any free source for the standard. Although by searching the Web, you can piece together more than enough EN 13537 standard information to use as a highly informed consumer.

On your second point, remember the torso blanket is used in addition to an existing quilt. The body is already completely insulated by the quilt and sleeping pad. The torso blanket is, primarily, further reducing natural convective heat loss. The torso blanket’s item clo is not higher because it is a small area. It is high because it provides 3″ of uncompressed 800 fill goose down. If the torso blanket covered the whole body, it would be approximately twice as warm.

800+ fill goose down is not only light for backpacking, it is also warmer for a given thickness. This is because it has less solid material to conduct heat and finer fibers to reflect more radiation. Solid materials, feathers and down quills, have a higher conductivity than still air.

The theoretical limit to the insulation provided by still air, at 32F, is about 6.8 clo / inch and the highest quality goose down (800+) = 6.6 clo / inch. By contrast, standard down (550) = 4.5 clo / inch, and Polarguard Delta = 3.1 clo / inch.

I am enjoying this thread.

I am getting ready to start work on a multi-use system of stuff to wear and sleep in that if all used at the same time would keep me warm down to (0) degrees F.

Some of the expected givens will be a Down Air mattress – bought or home-made to sleep on. Maybe a Bivy type item that would contain everything that might also be insulated in someway.
Maybe a small tent to use at night but at least some nights will be spent in a typical AT Shelter.

I want all this to be really light – as SUL as I can make it. The insulation I have to work with can be anything from 800+ Down to Polarguard Delta, Climashield XP or Combat.

Outside shell material that I have and can use are Pertex Quantum (.9 oz per sq yard), Momentum 90 (1 oz per sq yard) and Epic Malibu (1.7 oz per sq yard).

I want to make the different layers using “heat zone construction” if I can figure that out.

I expect some of the designs used may will seem strange but if they work that is all that matters.

Thanks.

Bill,

I think you are significantly along towards accomplishing your objective. Your down air mattress tube project should efficiently address bottom conductive and radiation losses. Your most recent ultra-light bivy/integrated Climashield Combat insulation project should address forced convection (wind) and dew-point issues. Based on your complete ensemble there will be a range of temperatures / humidity in which the dew-point should be in the Climashield or higher. This will allow you the option to use down without a vapor barrier for many environments. Even with a wet base layer and wind shirt you should be able to push the moisture past the down and into the Climashield layer or higher in a range of environments.

The key to the most efficient top insulation is to allow all of your clothing insulation layers to integrate into a quilt that is warm enough and wide enough to eliminate drafts. The converse of using a quilt for clothing insulation is not very efficient. This is because you don’t have layering granularity, forced convection (wind) is problematic, and the billows effect pumps the warm air out of the quilt /serape if you are moving. 800 fill down will be the lightest solution if you are going to camp in an environment where you can keep it dry.

The technique I use for multi-month expeditions to wet areas in Alaska is to zip together a synthetic jacket and two synthetic vests into a quasi-integrated quilt. I put my feet into one arm of the jacket to keep them warm and my head through the arm hole of the second vest and then loop the remaining material over my head to make a hood. A custom design as opposed to adapting a commercially made synthetic jacket and vests could be made to insulate much more efficiently as a quilt. You could eliminate the draft from arm holes in the vests, add draft tubes below the zippers to reduce drafts and engineer a tapered girth to match your custom quilt design.

For extremely wet environments Primaloft One is the best choice for clothing insulation. It has the highest clo/oz rating of the synthetics (.84), it drapes well, and it absorbs the least amount of moisture. Unfortunately I am not aware of any place that sells this material for DIY purposes. For your projects up to this point, Climashield XP has been the best solution. This is because you don’t have to aggressively stabilize continuous filament insulation. In clothing insulation each part of the garment is relatively small compared to a quilt or sleeping bag.

One way of accomplishing effective heat zones is to determine the item clo for each layer of insulation you may wear. You already know you need enough total clo for 0F. The difference in each zone can be augmented with supplemental insulation such as in your bivy top layer.

Thanks Richard.
You have given me several new thoughts and ideas to think about.

Now to see what I can come up with.

>>”The technique I use for multi-month expeditions to wet areas in Alaska is to zip together a synthetic jacket and two synthetic vests into a quasi-integrated quilt. I put my feet into one arm of the jacket to keep them warm and my head through the arm hole of the second vest and then loop the remaining material over my head to make a hood. A custom design as opposed to adapting a commercially made synthetic jacket and vests could be made to insulate much more efficiently as a quilt. You could eliminate the draft from arm holes in the vests, add draft tubes below the zippers to reduce drafts and engineer a tapered girth to match your custom quilt design.”

As the young’uns say: “How cool is that!”

Richard, that’s ingenious. I wondering about the weight, what do the three articles of clothing weigh and the lowest temp they are reasonably usable? Also, elastic arm holes on at least one of the vests to somewhat cinch it closer to neck while allowing expansion to get your head through it?

I’m guessing this is, in part, what Bill was referring to when he replied, “You have given me several new thoughts and ideas to think about.”. Can’t wait to see what Bill’s fertile genius comes up with.

We can’t buy the UL American stuff in Australia (not at any acceptable price, anyhow). So I made our own sleeping bags / quilts. I use mine purely as a quilt now.

Fabric: Pertex Microlight. 250 g (8.8 oz) with 40 mm (1.6″) walls.
Fill: 800 loft down, 300 g (10.6 oz).
Total weight: 550 g (19.4 oz).

This as a quilt keeps me warm down to a few degrees above freezing with only a silk liner – no clothes. With thermals on it works to about -5 C (23 F).

How?
I sleep on a GOOD Therm-a-Rest. Warm and comfortable!
It has a generous hood area which goes *right over* my head. No, I do NOT suffocate under it – or under my quilt at home either.
I wear a 200 weight fleece ski hat to bed as well.
I sleep next to my wife, who has a nearly identical bag. OK, we snuggle up when cold.
We are inside a tent, not under a tarp. No wind.

Works fine for us. Been in the snow with it. We were warm enough.

Paul-The Alaska rain forests layering example is an extreme case in which I adapted the synthetic clothing insulation I needed for purposes other than sleeping. I kayak the Gulf of Alaska as well as hike.

For more conventional backpacking endeavors, take one jacket and one vest from the same manufacturer’s product line to create a torso blanket. Normally this will insure that the vest and jacket zippers mate. Mixed manufacturer combinations may also work. Zip the jacket to the vest. Put the jacket at the bottom with your feet in one arm hole that is folded closed on the bottom to seal it. Take the second sleeve and insert it into the first vest arm hole to seal it. Fold over the top of the vest to seal the other arm hole.

The above approach results in a largely uncompressed torso blanket to augment your more conventional sleep system. It should be obvious if you just have either just a jacket or vest that this will also make a torso blanket but, the area will be smaller. The method to calculate the supplemental torso blanket insulation value for different insulation materials and sizes was covered by me earlier in this forum thread. You can put the torso blanket inside or on top of your existing sleep system. Put it where the combination maximizes the total loft.

Optimally, you need a minimum of 3/4 to 1″ insulation in your conventional sleep system that you are augmenting. This minimum will largely prevent radiation and forced convection heat losses for your complete body. The torso blanket will then primarily supplement the blocking of natural convection heat loss.

Outside of the Alaska rain forests I prefer high loft down. I normally wear size large jackets and vests but I wear size XL, with high loft down, because it will normally expand to eliminate the billows effect. Size XL then gives me a larger torso blanket area to augment my sleep system.

Roger-I am always happy when real world experience and technical theory match. It tends to give me more confidence in the theory <grin>. Even more importantly, when real world experience doesn’t match the theory, I learn more.

My most recent learning experience from you relative to this is when you recently posted on the topic of 100 weight fleece brands. You said in part, “…I wear a Taslan windshirt down to about 40 F – with a pack on. Below that to freezing I might add a light thermal for half an hour, until I warm up.” In addition to blocking the wind, a wind shirt can provide an air layer on the inside which results in a clo contribution about 8.3 times (what the intrinsic wind shirt material itself provides. I discovered that when I analyzed why your real world experience didn’t match my misguided understanding of the theory. Thank you for your objective analysis and frequent forum contributions.

> Although by searching the Web, you can piece together more than enough EN 13537 standard information to use as a highly informed consumer.

There’s plenty out there. Start at:
http://www.europeanoutdoorgroup.com/information/index.html
Halfway down the page you will see 3 PDFs starting with EN13537… Download and read them.

Also have a read of the PDF by Mammut at:
http://www.mammut.ch/mammut/uploadedFiles/Sleep%20Well_Pt1_E.pdf

This is arguably the best document on EN13537 and sleeping bag ratings which I have seen, world-wide.

Cheers
Roger Caffin

Hey Bill,
I am very interested in a better discription about your cs socks you made.
I may end up doing the the same
I made a 0.6″ Primaloft helmet style cover that completely covers my neck and head. It came in at 1 ounce and is super warm.
Making the socks shouldn’t come out to more than 1 1/2oz for the set and would be a better choise than bringing a 1 1/2oz pair of smartwools.