Author Topic: Sleeping bag liner  (Read 661 times)

SteamyTea

  • Veteran Member
  • *****
  • Posts: 913
Re: Sleeping bag liner
« Reply #15 on: 17:21:07, 22/06/20 »
Thermal losses happen 3 ways, conduction, radiation and convection.
Conduction is reduced by insulation.
Insulation is really a combination of a material with a high thermal resistance and small pockets of air (or other gases, and even no gases in the case of vacuum insulation) trapped between whatever material the insulation is made from.
This reduced the movement of the air, which reduces convection.
Air also has a fairly high thermal resistance.
The SI unit is kelvin meters per watt, R = K.m/W.
It is more usual to use the reciprocal 1/R, which has the SI units watts per metre kelvin, λ = W/m.K.
Air has a typical value of 0.0255 W/m.K, polyester has a value of 0.05 W/m.K.
Polyester and paper conducts at about twice the rate of air, 0.05 W/m.K.
Cotton conducts at about ten times the rate of air, 0.23 W/m.K.
Dry earth is even worse 1.5 W/m.K, 60 times worse, and is, in effect, an infinite heat sink.


As you cannot realistically change the ground temperature, or your body temperature, all you can do is increase the thickness of the insulation.
As clothes and sleeping bags compress when laid on, it is therefore best to use an inflatable mattress as this will drastically reduce the losses.
I don't use emojis, irony is better, you decide

Bigfoot_Mike

  • Veteran Member
  • *****
  • Posts: 1753
Re: Sleeping bag liner
« Reply #16 on: 17:59:01, 22/06/20 »
Still air is a good insulator. It is what makes our clothes feel warm and provides a lot of insulation to animals, trapped in their fur. It is also what makes double glazing work.  A camp bed doesn’t constrain the air and allows the air to circulate, so may not be as effective as the mattress.


Explained in more detail by Steamy Tea above.

gunwharfman

  • Veteran Member
  • *****
  • Posts: 4709
Re: Sleeping bag liner
« Reply #17 on: 17:59:45, 22/06/20 »
I once slept directly on the ground, I was a student, it was in Austria and I was drunk. I fell asleep, the drink made it possible but I woke up very soon freezing! I had a dreadful night, never repeated the experience since!

The nearest to it was last Nov 10th when I thought I would sleep in my car, I felt lazy and couldn't be bothered to organise my gear. I thought I would just wrap my quilt around me, recline the seat, and doze. was cold very quickly so I had to make the effort to make my bed properly. I blew my Neo Air up and then slept well.

SteamyTea

  • Veteran Member
  • *****
  • Posts: 913
Re: Sleeping bag liner
« Reply #18 on: 18:19:20, 22/06/20 »
I once slept directly on the ground, I was a student, it was in Austria and I was drunk. I fell asleep, the drink made it possible but I woke up very soon freezing! I had a dreadful night, never repeated the experience since!

The nearest to it was last Nov 10th when I thought I would sleep in my car, I felt lazy and couldn't be bothered to organise my gear. I thought I would just wrap my quilt around me, recline the seat, and doze. was cold very quickly so I had to make the effort to make my bed properly. I blew my Neo Air up and then slept well.
I had my car break down in rural Oxfordshire a few years back.
It was -3°C.
I was so cold I thought I was going to die.
I don't use emojis, irony is better, you decide

Birdman

  • Full Member
  • ***
  • Posts: 100
Re: Sleeping bag liner
« Reply #19 on: 11:19:25, 23/06/20 »
I'm using a silk liner.


It adds some extra warmth, but not much. Main advantage for me is that it keeps my (expensive, down) sleepingbag more clean. I do lots of long-distance walking where you often cannot wash yourself properly for weeks on end, so it is nice to have a liner that is easy to wash/ rinse and dries fast (and you can do so while on the trail).


Another thing that I like is that it makes your sleeping system more flexible. If it is warm, I just sleep in the liner.


An last but not least, I like the feeling of silk on my skin. Really an A+ sleeping experience on the trail!
My travel and walking reports: https://www.hikingbirdman.com/

Birdman

  • Full Member
  • ***
  • Posts: 100
Re: Sleeping bag liner
« Reply #20 on: 11:27:59, 23/06/20 »
What I was trying to suggest is that a mattress like my NeoAir also helps me to keep warm.


Indeed! The mattress is so important to keep you warm. So much heat is lost through the ground.


The NeoAir is excellent. I have both the Xlite and the XTherm. Xtherm is my favourite, if I had to buy only one. You'll be nice and warm even when sleeping on solid frozen ground. But I have used the Xlite at -3°C and wasn't cold.
My travel and walking reports: https://www.hikingbirdman.com/