Thread: Technical Note on Canvas for Extreme Cold

1. Technical Note on Canvas for Extreme Cold

I thought I would explain something that has become clear to me lately.

FourDog and others say, "20*F and below, use breathable footwear and outerwear. 20*F and above, use waterproof footwear and outerwear." Sometimes they use 10*F as the breakpoint. Whatever temperature you use, the concept is intuitively obvious. Still, I wondered, why won't other materials work as well? Why canvas?

There have been several threads on the continuum of waterproof vs breathable. There is a third leg to that stool: windproof. Canvas is highly windproof and highly breathable. Untreated canvas doesn't handle water well. Other fabrics are water resistant, windproof and breathable, but none are as windproof and as breathable as canvas. Why does that matter?

It all became clear to me when I realized what temperature differential we have between our bodies and the ambient conditions. At -15*F, there is a 100 degree difference between our skin and the air! If it's 85*F at your skin, and -15*F outside, that's 100*F difference... that's huge! Still, why does that make canvas so special?

Everyone has heard that nature abhors a vacuum. Nature also abhors a differential. When ever there is a difference in something across a boundary, there is a natural driving force to level it out. This works with water levels, salt concentrations, and many other things, including temperature differences.

Temperature differential is the driving force of heat transfer. The higher the temperature differential across an insulator, the more heat will be lost through the insulator. What makes this important in extreme cold weather is the other differential, which works hand in glove with temperature: humidity.

Inside your toasty nest, it could be 50% relative humidity or higher. Outside your hammock and all of your insulation, it could be -15*F and 30% relative humidity or much lower. That is a relative humidity differential of 20% or more. However, it is a much larger humidity differential that you would think, just looking at relative humidity.

At 50*F and 50% relative humidity, the absolute humidity is 25 grams per cubic meter, and the dew point is 26*F. Compare that to -15*F and 30% humidity, where the absolute humidity is 0.5 grams per cubic meter. Using absolute humidity, which measures the actual amount of water in the air, there are 25 grams per cubic meter inside your hammock, and only a trace of water vapor in the air outside! That is a gigantic difference.

So, what happens is the temperature and humidity differences work together to drive both heat and moisture out of your hammock, right through your insulation. The result is both heat loss and condensation. There is no way to avoid either in such extreme conditions. Heat loss can be minimized by using lots of insulation. Condensation can be minimized, too. How? By using breathable insulation with canvas outside! (You saw that coming, right?)

The canvas will keep out the cold wind, but allow the moisture through. The trick is to get most of the moisture to go right through your insulation in the vapor phase, without condensing and making ice. For that to happen, a highly breathable outer layer is required. Canvas doesn't inhibit the flow of water vapor through your insulation, so it allows the water vapor to escape into the air without much condensation.

Of course, your clothing and hammock insulation must be breathable for all this to work. For instance, if you have a vapor barrier under your hammock, that stops the moisture cold, so to speak. With luck, you won't find ice crystals there when you hang in Minnesota!

Think about what happens if you use waterproof boots in extreme cold. There is a lot of water generated by your feet when you are active. ("Over 2 cups per day!" says FourDog.) If your boots are waterproof, that water stays in. It gets into your socks and the insulation of your boots. Then, you remove your foot and go to sleep. If you don't dry out the inside of your boots, all that water will freeze. OTOH, canvas and leather mukluks are highly breathable, so the moisture goes right out into the ambient air, so that socks and liners are relatively dry when you remove your feet.

Extreme cold air will dry you out fast. That's why we have to rehydrate more than normal in those conditions. We make that attribute work to our advantage when we use breathable insulation covered with canvas. We get that cold air to pull the moisture right out of our insulation, without condensing, so that our insulation doesn't collect ice crystals, and remains in top condition to keep us warm.

Of course, there is another side to this story, and I welcome folks to explain that as well. I just wanted to explain what I have learned about breathable systems with canvas, and why it works. It has been a lot of fun making traditional anoraks, mukluks and hammock socks using canvas, and seeing them work just like they are supposed to do. I hope this helps folks understand why.

- MacEntyre

2. Excellent presentation! 'Nuf said

3. So, with this information in mind, what are the best methods to keep yourself warm AND travel light a)on your person? and b)for hammocking?

I've been eyeballing the anoraks and such from Empire Canvas.
But I keep thinking about the weight. And how that stuff doesn't do double duty.

I like that my Driducks poncho is somewhat breathable and can be strung up under my hammock and underquilt for a small boost. But is it breathable enough under 20º?

And my guess is that IX would fall into the over 20º category then, right?
Or does it breathe well enough in most cases?

4. Thanks for the write-up.

5. Originally Posted by RAW
So, with this information in mind, what are the best methods to keep yourself warm AND travel light a)on your person? and b)for hammocking?
Many people this winter have commented that without a pulk, they would be hard pressed to pack all their stuff! The bulk is mostly down, though.

I wear my canvas anorak and mukluks, so the only canvas item I would pack would be a canvas sock. (I'll have one for Roan Mtn.) It's about 100% heavier and 50% bulkier than an IX Hammock Sock.

Originally Posted by RAW
I've been eyeballing the anoraks and such from Empire Canvas. But I keep thinking about the weight. And how that stuff doesn't do double duty.
I used the anorak to cover the foot end of my hammock. What more do your waterproof boots and poncho do for double duty?

Originally Posted by RAW
I like that my Driducks poncho is somewhat breathable and can be strung up under my hammock and underquilt for a small boost. But is it breathable enough under 20º?
I think not, or at least not breathable enough to take this approach.

Originally Posted by RAW
And my guess is that IX would fall into the over 20º category then, right? Or does it breathe well enough in most cases?
Correct!

However, Canoeski had good results using a Baby Orca right under his hammock in MN. Thing1 and I did the same at Mt Rogers. It doesn't block all the vapor, since it's a 3/4 UQ.

FourDog used a piece of reflectix right inside his hammock, so his rig was not completely breathable. At any rate, if you do use a vapor barrier, it should be right under you or your hammock. Any further away is asking for condensation and ice crystals.

In MN, I had no vapor barrier of any kind in my SnugPod.

Excellent presentation! 'Nuf said
Thank you!
Originally Posted by Rug
Thanks for the write-up.
You are entyrely welcome!

7. Thanks John. I'm glad to see this being talked about more. The truth is for any activity where there is exertion so that you sweat, not talking about rain here, there has not been anything made in decades to replace the abilities of natural fibers. For walking across the street to your car or around town fine but for work/workout , no. Most of the products on the market today are made for the middle class consumer market that get out on the odd weekend. Their fashionable, neat colors with cool names. I get nostalgic for the days when so many of my friends wore Stanfield grey label underwear tops and wool pants. We would work hard and when we rested you could see the steam just pour up from our bodies. I still do this and won't win a fashion contest. Modern fabrics have their place, i have some, and its a process to figure it all out.
I think a cotton anorak could be useful for "cool" temps as well when your hiking , no rain or snow, and you stop for lunch and dawn your anorak to protect you from wind chill but still breath. JMO
bill

8. So, next question:

Where's the magic compromise for canvas weight/thickness?
Thin enough to not weigh 10#, but thick enough to block wind/trap heat.

9. Originally Posted by mbiraman
Thanks John.
You are entyrely welcome!

Originally Posted by mbiraman
...the middle class consumer market that get out on the odd weekend.
FourDog and I talked about that... for "weekenders," which most of us are, it doesn't matter as much. But for spending days in the woods, or in a survival situation, your gear becomes critical, and breathable fibers shine in extreme cold.

Originally Posted by RAW
Where's the magic compromise for canvas weight/thickness? Thin enough to not weigh 10#, but thick enough to block wind/trap heat.
As light as possible! You could make an anorak from tightly woven cotton bed sheets, although that's a little too light for me. It's hard to find Egyptian cotton canvas, which is a little heavier than a bedsheet, but I have come very close with a local source.

10. Canvas: OKPIK BSA instruction in January

I returned from my second OKPIK week at the Northern Tier High Adventure Base in Ely, MN. By the way, OKPIK is Inuit for "snowy owl" - a creature that is comfortable in the cold North. Anyhow...I took my Gortex parka and Sorel boots with removable liners. Here is what I found...

Warm moisture from our bodies will move away from our skin and into our layers only until the warm moist air comes into contact with cold air. When I wore Gortex (this trip was between a low of -24 and a high of 0) the Gortex did not breathe! The pores stopped up with the frozen moisture! In fact I felt very clamy. When I switched to my canvas Anorak and the canvas mukluks instantly I found the solution to arctic cold camping!!!

The canvas enabled the moisture to escape ("breathable) and I was not clamy the rest of the week. It was amazing! The canvas pores are larger than the Gortex and therefore more breathable! If you go to Stegers Mukluks in downtown Ely, you will look at their boots (as I first did) and you will say "I thought cotton kills? How can this canvas boot keep my feet warm and dry?"

Here is the deal: The BSA classifys winter camping into three categories; 50 to 32 degrees, 32 to 15 degrees and below 15 degrees. Here in East Tennessee it rarely goes below 0. So, we wear Gortex since our snow is WET and there is a higher cahnace of rain, sleet and wet snow. In Minnesota we never saw a day above zero. The snow was DRY! It is not going to melt unless I melt it!

So, IF I stepped in slush on a lake all I had to do was put snow on my boot and the snow absorbed the water and my boot became dry! My Sorel (if wet) would not have dried for a long time.

So....LONG LIVE CANVAS FOR EXTREME COLD AND DRY SNOW!