2

I know there are usually two different sides for an emergency blanket to be used depending on how you want to use it (i.e. "protecting" from cold or, the opposite, from heat).

Having a thermal camera, I tried to see which side is reflecting the most heat so I could identify the side to use for keeping the person warm inside. I was expecting the silver side to be the correct one (as almost always stated).

And surprise ! It's the opposite: gold one seems to reflect better IR than silver do, like a true heat mirror (see pictures).

Am I missing something in the experiment ?

Thermal view of emergency blanket

Normal view of emergency blanket

4
  • Actually not, I saw this post but it always states the silver side to be the most reflecting one, which is the opposite from what I've tested so far, but thanks ;) But you're right in the way that I should may be open a discussion in this post ? Jul 7, 2022 at 7:23
  • It's not a "discussion" site, but, can you distinguish radiated heat (bad) from reflected heat (good)? In the offered duplicate it says these are not "blankets" and they do not keep you warm. Jul 7, 2022 at 7:50
  • While not the same question in your view, it is so closely related that we do see it as a duplicate on this site. The science behind it would likely fit on an other Stack Exchange site but I do not think that we can move the question as it is now, it would not fit one on one. Look at the science related sites to find one where it fits.
    – Willeke
    Jul 8, 2022 at 15:13
  • 1
    I am not sure but if you are "reading" the temperature of the object and the object is reflective it will be cooler, the point of the blanket is to reflect your heat back at you
    – Barreto
    May 1, 2023 at 19:24

2 Answers 2

3

So since your question is "what did you miss in your experiment", a few things I can think of:

  • The blanket seems to be folded which is not the real application of the blanket. Stacking multiple layers may or may not change the results. I have no idea, but the blankets are not 100% reflective, i.E. some IR gets through the first layer.
  • Use a proper setup. Strictly speaking, what you measured is the "current surface temperature (within measurement error of you IR cam) of a folded blanket". For all we know, you just held the gold side in your hand for a couple of minutes and it heated up more than the other side. Reflections from other objects nearby can also disturb the measurement. This is a known issue with IR cameras.
  • There is more to reflexion than IR. Visible and UV light also contribute to heating.
  • Usage might be dependant on emission/absorption and temperature of the human body compared to the surrounding environment.

Also I'm not sure if reflection is actually the proper measurement here. I'm thinking, you basically want to stick a thermometer in the blanket with the gold/silver side out and leave it in the sun/freezer for an hour or so. Which is more or less what the people from this paper did.

Now, to the second part of the question: Which side up? The results from the paper (and a few other sources across the web) basically say: It really doesn't matter. Reflectiveness between gold and silver varies by just a couple % and depends on the manufacturer.

it does not matter whether silver is turned down or not. There are several factors to be considered, including convective and conductive effects, vapor barrier function, and distance and moisture between the body and the blanket

This is in line with my personal experiences when given an emergency blanket after cold races. The main benefit in those cases is that you can wrap the blanket airtight around yourself and reduce convection. It doesn't magically turn hot or cold when you use the "wrong side".

2

I have looked into this in the past, and the best answer I have found is that it varies by manufacturer. I do know at least one company has made gold the more heat reflective side. f your heat gun is giving you a clear answer, I'd go with that, but if you have other blankets from other manufactures, check those too. The one fairly certain point is that if one side is shiny and one dull, the dull side can be assumed to be less reflective. If they are different colors of shiny, check the package, or do what you did and use a heat gun to check.

Not the answer you're looking for? Browse other questions tagged or ask your own question.