View Full Version : Rollmat question!?
Ok an odd question maybe but does anyone out there own / use a 'silver' rollmat? and more importantly which side do you sleep on?
Silver side up - to reflect your heat back or
Silver side down - to 'reflect' the cold from the ground away?
I have to say I personaly don't have one / have never used one and the question has come from swmbo following a weekend camp with her Scouts where they couldn't come up with a consensus:rolleyes:
I reccon Silver side up but can see the rational behind having it down, what do you think?
BushTucker
23-11-2007, 15:47
I would have thought silver side up, I would want to keep the heat but surely if siver side down then the cold would be pushed away and surely the warm foil would also reflect the heat away into the cold....
Dunno, just a thought
I would side with you on that one, the silvering is to reflect heat towards you, cold is just an absence of heat. I suspect that it'd be warmest silver-side up, but guess it would still work silver down if only to help keep the heat within the insulation of the rollmat itself which might give a gentler heating effect.
gregorach
23-11-2007, 15:51
Cold isn't something you can reflect - it's not a thing in itself, it's just the absence of heat. You can no more reflect cold than you can reflect darkness.
I'd go for silvered side up in theory, but in practice I would expect that it'd take some pretty decent scientific instrumentation to notice the difference. You don't lose much heat through your mat by radiation, you lose it by conduction.
John Fenna
23-11-2007, 16:31
Silver side down is even slippery-er than a normal mat on your average groundsheet...dont know if it has any effect on its thermal qualities though...
I voted no difference
In 1984 two top Canadian anaesthesiologist did a series of experiments with twelve healthy volunteers, testing the thermal insulation properties of metallised plastic sheeting, (which is a 10 µm thick Mylar sheeting with thin aluminium coating.) Clear polyethylene sheeting and 100 per cent polyester thermal bed blanket.
The experiments were carried out on individual subjects sitting in a whole body calorimeter and covered first with a thermal bed blanket bag up to the neck. Then the three materials were tested, one at a time, over the original thermal bed blanket up to the neck. The temperature of the calorimeter was set at normal ‘operating room’ temperature of 18° C. Metallised plastic sheeting provided the greatest reduction in sensible heat loss of all three materials tested.
Over all they found that, there was a 29.7% saving in body heat between having nothing (or just a blanket) covering you and being covered by the metallised plastic sheeting, there was a 20% saving when just covered in a thermal bed blanket, and a similar reading for just being covered in a clear plastic sheet (19.3%) . I take to mean that difference between the three is about 9.7% saving.
However, their findings concluded.
“The reflective surface of the metallised plastic sheeting acts to reduce radiative (the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system) heat loss from the body, while the very nature of the sheeting decreases convective heat losses by eliminating draughts”.
So most of the saving was made by keeping the ‘subjects’ out of the ever-present draughts.
Since then several others have also concluded that wrapping a body in clear plastic sheeting is just as efficient as Mylar, both, on paper at least, have testable benefits. However, a pre-warmed blanket provide as much protection over heat loss.
One problem that was found in the experiment was the amount of water vapour that condensed on the inside of the plastic materials (the anaesthesiologists recommended not using the Mylar and the plastic near any electrical equipment)
Working on the theory that you fit the same sort of stuff (closed cell foam with silvered finish to one side) to the walls of your house behind the radiators (silverside towads the radiator) I'd say shiney side up.
Chris
Silverside up, but then again don`t know, how much difference can it make if you`re laid on a cold floor anyway ?? Silverside up though just in case :cool:
I don't think it would make any measurable difference. (voted this way!)
BUT ... if I had one I would put it silver side up.
Simon
Northern Giant UK
25-11-2007, 15:09
I can't vote cos my solution isn't there.
Due to the weight (or lack of it) of these mats i'd go for both!
Anyone with a back as bad as mine would probably take 2 mats and my solution would be to have the bottom mat silver side up and the top mat silver side down and if that doesn't give an effective insulation nothing will :)
Size shouldn't be a problem as you can strap them on the outside of your pack.
Kev
Cairodel
25-11-2007, 16:47
Why not use mats that are "silvered" on both sides. I use them here under a sleep mat
during the winter mumfs.... gets unbelievably cold...
Neanderthal
25-11-2007, 17:44
I'd say silver side up to reflect body heat, rather that silver side down. Things get colder due to loss of heat rather than absorbing cold.
Probably something to do with the second law of thermodynamics.
Anyone remember Moon Bags? A thin sleeping bag with a layer of aluminium foil sewn in. They were rubbish but packed small. :)
Stu
I doubt it makes any real difference.
Anyone remember Moon Bags? A thin sleeping bag with a layer of aluminium foil sewn in. They were rubbish but packed small. :)
Stu
Yes, suffered a week in January in Brecon in one of them.
I'd go for silver side up to reflect the bodies heat back at you, but why bother with those fancy mats when a 2nd hand Brit Army mat will do the job for you!
I slept out at -30 Celsius (and then some!) with the army mat and got on fine...:rolleyes:
I'd go for silver side up to reflect the bodies heat back at you, but why bother with those fancy mats when a 2nd hand Brit Army mat will do the job for you!
I slept out at -30 Celsius (and then some!) with the army mat and got on fine...:rolleyes:
Until I got the thermarest I uses to use a true karrimat and was more than happy for years!
The question arose as a couple of scouts had them and they began to argue as to who was right! :lmao: ....... suffice to say the poll has more or less confirmed that I was right! (phew ;) )
Until I got the thermarest I uses to use a true karrimat and was more than happy for years!
The question arose as a couple of scouts had them and they began to argue as to who was right! :lmao: ....... suffice to say the poll has more or less confirmed that I was right! (phew ;) )
Fair one mate!:D
John Fenna
01-12-2007, 14:39
Are there any silvered "self inflating mats" around?
Which side up should these be used?
I have single-handedly now extended the life of what has to be the most contentious and futile thread discussion around!
Excepting Reds "light - bulb" one....
:D :D :D :D :D
Evil laughter echoes around the globe....
Merry Xmas!
John
Are there any silvered "self inflating mats" around?
Which side up should these be used?
http://chinasources.en.alibaba.com/product/50062628/50811350/Camping_Equipment/EVA_Camping_Mat.html Silvered! :D
Sounds like a ultralight sleeping mat... :D
http://nbweinuo.en.alibaba.com/product/50380799/200783791/Household_Products/aluminum_foil_sleep_mat.html
Heh, this one is off topic.. but seems not a bad idea for bivvying maybe..
http://chinasources.en.alibaba.com/product/50062628/50970131/Camping_Equipment/Sleeping_Mat_with_Shelter.html :D
John Fenna
01-12-2007, 16:07
Nah - they ain't self inflating - just foam!
Silver thermarest types is my prey!
silver side up to reflect heat to you .dont think yuo can reflect cold