Author Topic: Sleeping mat matters  (Read 2184 times)

gunwharfman

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Re: Sleeping mat matters
« Reply #30 on: 11:10:46, 24/06/18 »
The X frame seems to have lots of gaps to let cold through? Even in your sleeping bag can this be a problem or do you have to ensure you have something else underneath you as an insulator? With so many edges do you get airleaks more often?

I couldn't use one because I use a sleeping quilt which does not have a back or a hood.

marmottungsten

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Re: Sleeping mat matters
« Reply #31 on: 19:20:49, 24/06/18 »
The X frame seems to have lots of gaps to let cold through? Even in your sleeping bag can this be a problem or do you have to ensure you have something else underneath you as an insulator? With so many edges do you get airleaks more often?

I couldn't use one because I use a sleeping quilt which does not have a back or a hood.


I place an ultralight space blanket on the floor of the tent, and the sleeping bag goes on top of that.  It offers great thermal insulation by reflecting my body heat back up towards me, rather than allowing it to escape to the cold ground under the tent.  A space blanket is very light and only costs about 80p on ebay, so it was a no brainer to me.
It's wider than the floor of my tent, so when I want to warm up faster I can simply flip the rest over my sleeping bag, then flip it away again if I get too hot.  You don't need to fold it carefully, I just scrunch it up into a ball and throw it my Trekmates 8L compression sack along with my tent.

richardh1905

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Re: Sleeping mat matters
« Reply #32 on: 20:06:20, 24/06/18 »


I place an ultralight space blanket on the floor of the tent, and the sleeping bag goes on top of that.  It offers great thermal insulation by reflecting my body heat back up towards me, rather than allowing it to escape to the cold ground under the tent.  A space blanket is very light and only costs about 80p on ebay, so it was a no brainer to me.
It's wider than the floor of my tent, so when I want to warm up faster I can simply flip the rest over my sleeping bag, then flip it away again if I get too hot.  You don't need to fold it carefully, I just scrunch it up into a ball and throw it my Trekmates 8L compression sack along with my tent.


A space blanket would make a good footprint, perhaps.

marmottungsten

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Re: Sleeping mat matters
« Reply #33 on: 21:04:27, 24/06/18 »

A space blanket would make a good footprint, perhaps.


Possibly...The plastic film it's made seems quite tough but it's also very thin and would probably get pierced easily by sharp objects, like broken off twigs or split stones, if used under a tent.  That probably wouldn't stop it's insulation properties but it might let groundwater in through any holes it might get. 
As my tent already came with a footprint,  the thought of using the space blanket under my tent never came to my mind.

richardh1905

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Re: Sleeping mat matters
« Reply #34 on: 07:48:54, 25/06/18 »


Possibly...The plastic film it's made seems quite tough but it's also very thin and would probably get pierced easily by sharp objects, like broken off twigs or split stones, if used under a tent.  That probably wouldn't stop it's insulation properties but it might let groundwater in through any holes it might get. 
As my tent already came with a footprint,  the thought of using the space blanket under my tent never came to my mind.


Think that I'm going to give it a try; I don't bother with a footprint as I have a cheapo tent, which, as you know, is quite heavy enough. If the space blanket gets wrecked, it hardly matters; they cost next to nothing.

NeilC

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Re: Sleeping mat matters
« Reply #35 on: 08:30:47, 25/06/18 »
Reflectors don't work when covered in a material that does not allow radiation to pass, in the same way that a mirror doesn't work if you throw a sheet over it. So they're pointless under a sleeping bag. You need an air gap between the reflector and the source of heat radiation.
« Last Edit: 09:14:59, 25/06/18 by NeilC »

April

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Re: Sleeping mat matters
« Reply #36 on: 08:58:40, 25/06/18 »
You shouldn't be envious of people using sawn off mats, you should pity them, for they know not what they are missing!  :D

Well I use a sawn off foam mat and a 3/4 thermarest prolite. I sleep on my side in a foetal postion. I am happy with me set up, I am very comfortable and sleep like a log. MT you have to realise not everyone is the same, your mat might suit you but it won't suit everyone. I wouldn't use your mat if I was paid to do so.
"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

KimE

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Re: Sleeping mat matters
« Reply #37 on: 12:24:32, 25/06/18 »

"Made from lightweight 15D UltraSil®"[/color][/font][/size]
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The sea to Summit mat may go from 90£ to 0£ in value in a very short time, and it lacks insulation.[/color][/font][/size]

richardh1905

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Re: Sleeping mat matters
« Reply #38 on: 14:27:09, 25/06/18 »


Reflectors don't work when covered in a material that does not allow radiation to pass, in the same way that a mirror doesn't work if you throw a sheet over it. So they're pointless under a sleeping bag. You need an air gap between the reflector and the source of heat radiation.

My motive for considering using a space blanket as a footprint is not heat saving, by the way; it is purely for physical protection of the groundsheet.

marmottungsten

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Re: Sleeping mat matters
« Reply #39 on: 00:26:04, 26/06/18 »
No delete button?
« Last Edit: 00:38:43, 26/06/18 by marmottungsten »

marmottungsten

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Re: Sleeping mat matters
« Reply #40 on: 00:35:23, 26/06/18 »
Reflectors don't work when covered in a material that does not allow radiation to pass, in the same way that a mirror doesn't work if you throw a sheet over it. So they're pointless under a sleeping bag. You need an air gap between the reflector and the source of heat radiation.


They are NOT pointless under a sleeping bag, especially under down sleeping bags, because the down in the bottom of the sleeping bag gets compressed by your body weight, greatly reducing it's insulation properties...In other words, it allows heat to escape from the bottom of the sleeping bag far faster than it can at the top, where the down is uncompressed.  So putting a space blanket under a down sleeping bag is the lightest and easiest method to reflect this otherwise lost body heat back upwards, thereby keeping you warmer.
« Last Edit: 00:39:40, 26/06/18 by marmottungsten »

NeilC

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Re: Sleeping mat matters
« Reply #41 on: 08:41:55, 26/06/18 »

They are NOT pointless under a sleeping bag, especially under down sleeping bags, because the down in the bottom of the sleeping bag gets compressed by your body weight, greatly reducing it's insulation properties...In other words, it allows heat to escape from the bottom of the sleeping bag far faster than it can at the top, where the down is uncompressed.  So putting a space blanket under a down sleeping bag is the lightest and easiest method to reflect this otherwise lost body heat back upwards, thereby keeping you warmer.


With respect, you've missed the point I made. Obviously one needs insulation under a sleeping bag, nobody would argue any different. It's just that reflectors don't work without an air gap. So there is little point in the reflective mat without an air gap, other than any other insulation it happens to provide.

Your mat is one design that it could help a lot with because it has so much space between the tubes but only if you have the mat placed in such a way as to create air for reflector to work with. I seem to remember you said you used your mat inside your bag, in which case you'd want the reflector also inside the bag and under the mat.

Actually there is more flexibility than that because shiny surfaces are also very poor emitters of radiation. So you can put one, shiny side out, to say line a hammock and it will reduce the radiation heat loss a lot but this also needs to be facing the air to work. The Ridgerest design benefits from this as it is ridged on both sides creating air gaps in both directors and I think they claim something like a 10% increase in R value.

See: http://www.radiantbarrierguru.com/new-videowhy-is-an-air-gap-required-for-radiant-barrier-to-work/


« Last Edit: 09:04:48, 26/06/18 by NeilC »

richardh1905

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Re: Sleeping mat matters
« Reply #42 on: 08:51:18, 26/06/18 »


Good explanation, Neil.


If the sleeping bag touches the foil, then heat is lost through conduction, negating the effectiveness of the foil. If there is an air gap, then conduction cannot occur, and the foil will reflect say 95% of the heat back (there will also be losses by convection within the air gap, but these will be minimal).


Having said that, the sleeping bag will not make perfect contact with the foil, so it will be of some benefit. Indeed, some foam mats have a layer of foil on one side.

NeilC

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Re: Sleeping mat matters
« Reply #43 on: 09:33:38, 26/06/18 »

Good explanation, Neil.


If the sleeping bag touches the foil, then heat is lost through conduction, negating the effectiveness of the foil. If there is an air gap, then conduction cannot occur, and the foil will reflect say 95% of the heat back (there will also be losses by convection within the air gap, but these will be minimal).


Having said that, the sleeping bag will not make perfect contact with the foil, so it will be of some benefit. Indeed, some foam mats have a layer of foil on one side.


Sorry Richard I just posted another reply whilst you wrote this so I'm out of sync.


But yes, any air gap will let it work, where that gap exists. However I wanted to see how much a sleeping bag flatted out so tried pressing up against a glass door and even laid over a glass coffee table in my down bag (OK I might be a bit of nerd!) and it flattens out very well unfortunately - very few and very small air spaces that I could see. Different bags may crinkle up more perhaps?


Slivered mats that are ridged will work much better hence the Thermarest designs, and there are orientations one can think of that do produce air gaps. My own sleeping mat has vertical baffles so there are gaps between them so under that on a flat groundsheet would help a little. But people sticking a reflector under a flat pad, or lying on a space blanket thinking it will "reflect their bodyheat" are generally wasting their time. I'm not convinced about silvered flat mats. Call me cynical but just because a company sells something, doesn't mean it works  ;D


I looked up human heat loss a while back and according to a medical paper looking at people in surgery, a naked person in still air loses most of their heat through radiation. I was surprised. But then it's not often we lay there uncovered in still air whilst camping. I think we all know from experience that the major loss downwards is conduction.
« Last Edit: 09:47:52, 26/06/18 by NeilC »

marmottungsten

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Re: Sleeping mat matters
« Reply #44 on: 00:18:09, 27/06/18 »

With respect, you've missed the point I made. Obviously one needs insulation under a sleeping bag, nobody would argue any different. It's just that reflectors don't work without an air gap. So there is little point in the reflective mat without an air gap, other than any other insulation it happens to provide.

Your mat is one design that it could help a lot with because it has so much space between the tubes but only if you have the mat placed in such a way as to create air for reflector to work with. I seem to remember you said you used your mat inside your bag, in which case you'd want the reflector also inside the bag and under the mat.

Actually there is more flexibility than that because shiny surfaces are also very poor emitters of radiation. So you can put one, shiny side out, to say line a hammock and it will reduce the radiation heat loss a lot but this also needs to be facing the air to work. The Ridgerest design benefits from this as it is ridged on both sides creating air gaps in both directors and I think they claim something like a 10% increase in R value.

See: http://www.radiantbarrierguru.com/new-videowhy-is-an-air-gap-required-for-radiant-barrier-to-work/


I don't think you realise how Infra red radiation propagates Neil...It does not need air to travel through at all...It will happily travel through a vacuum...For instance the heat from the Sun that we feel on Earth...It is infra red radiation from 93 million miles away, despite there being a deep vacuum between the two.  And Space blankets (or Mylar, to give it it's proper name) is highly reflective to infra red radiation...That is why they work as emergency blankets, despite being extremely thin.  When you wrap one around yourself it reflects the body heat you are radiating back towards you, keeping you warm...And it does exactly the same under a sleeping bag!