Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Simple Simon on 21/10/2016 06:51:22

Title: Would a Mylar sheet with holes to allow some heat to pass prevent over-heating?
Post by: Simple Simon on 21/10/2016 06:51:22

I have heard mylar blankets can trap some 90% of your body heat. The issue being, they're so good at it, they can also cause overheating, and I understand this as the reason we don't see the material used more widely than it already is. This made me wonder, however.

Could you poke minuscule holes in the mylar, so that it only traps 85%, or 70%, or 50% of the heat? Then, perhaps, you could have overlapping layers of mylar, and a simple adjustment could let you control this?

I expect this is a stupid question, and I apologize. I don't know much about how heat radiates. The issue I see with this idea is that, say the air was at -30C, traces of that could get through the tiny holes so that it's not a matter of 50% of the heat escaping, but of 50% of your heat escaping and cold air absorbing heat as well.


If someone could please help me to understand this, I would appreciate it. Thank you.

Title: Would a Mylar thermal blanket with holes to allow some heat through be feasible?
Post by: chris on 21/10/2016 08:06:46

Quote from: Simple Simon on 21/10/2016 06:51:22

I have heard mylar blankets can trap some 90% of your body heat. The issue being, they're so good at it, they can also cause overheating, and I understand this as the reason we don't see the material used more widely than it already is. This made me wonder, however.

Could you poke minuscule holes in the mylar, so that it only traps 85%, or 70%, or 50% of the heat? Then, perhaps, you could have overlapping layers of mylar, and a simple adjustment could let you control this?

I expect this is a stupid question, and I apologize. I don't know much about how heat radiates. The issue I see with this idea is that, say the air was at -30C, traces of that could get through the tiny holes so that it's not a matter of 50% of the heat escaping, but of 50% of your heat escaping and cold air absorbing heat as well.


If someone could please help me to understand this, I would appreciate it. Thank you.

Title: Re: Would a Mylar sheet with holes to allow some heat to pass prevent over-heating?
Post by: Simple Simon on 21/10/2016 08:29:18

You mean to say I have answered my own question? That I have described it correctly?

If that is the case, I would want to poke holes in the mylar, then cover those holes with air-tight, less heat-retaining materials.

Let's say we poke holes in the mylar sheet till 50% of the heat escapes, then we cover the holes with a material capable of trapping 10% of the heat. 55% of the heat would thus be retained? And if the material is airtight, you shouldn't have the issue of air getting in and absorbing heat from your body.

It could start to freeze the material, and if it does make the material cold that will start to cool the air inside the suit, which will effect the wearer. The issue being, it appears all low heat retention materials will suffer from this (cold is, after all, the removal of heat, and the material was selected for heat to be removed through it)?

There could still be some happy medium for this process, perhaps. Though it may just as easily be reached. by using a single material of a specific heat retention value.


Does this sound like a correct train of thought?

Title: Re: Would a Mylar sheet with holes to allow some heat to pass prevent over-heating?
Post by: Colin2B on 21/10/2016 08:53:22

Do you mean the emergency space blankets?
They also have a reflective surface which keeps heat in so it's not just conducted and convection loss that is being prevented. Also, the ones I've used tend to crackle when you move, not good for getting to sleep unless you are exhausted.