Aluminum foil reflectivity

Xringer · 01-10-17, 04:02 PM

I was thinking about Aluminum foil reflectivity, after I noticed that I could
feel heat on my face from the foil coated insulated foam.
I knew the foil wasn't warm, but I could feel heat from it..
It took a few seconds to realize that 'heat' was radiating from my face..
It was bouncing back from the mirror effect of the foil..

Then, I googled and found some stuff that's even more reflective! Mylar Reflective Film!
https://www.amazon.com/VIVOSUN-Horti.../dp/B018VI77QW

So, as I sit here in this small room, with two windows next to me,
I'm wondering if the heat from my body, wifi router and computer system,
is radiating towards that cold window, and escaping from this little room??

Does the warm air moving around inside this room emit IR radiation?
And would that emitted radiation be reflected back into the room, by Mylar foil?

The idea is to cover the windows at night, with a sheet of coroplast,
with a coating of Mylar reflective film, to reflect heat away from the windows.
(It would also keep air-flow on the windows lower)..

I've heard those Space Blankets https://en.wikipedia.org/wiki/Space_blanket
actually work pretty well..
And, I could turn the Coroplast-Mylar around backwards on hot sunny days..
Keeping my little computer room cooler in the summer..

Your comments please!

natethebrown · 01-11-17, 09:17 AM

Thermal radiation is a function of temperature.

https://en.wikipedia.org/wiki/Stefan...3Boltzmann_law

You probably did experience some heating from the radiation reflecting back at you. Those mylar "blankets" they give marathon runners after the race do work...to an extent. Once the mylar touches the skin, you can feel that it isn't helping you keep that warm because thermal conductivity & thermal convection sucks the heat away quicker. For your window, your absolute best value would be to insulate it with insulation to dramatically decrease both conduction and convection. I believe these foam boards even have the Mylar film on them:

https://www.lowes.com/pd/Expanded-Po...875-ft/3365568

jjackstone · 01-11-17, 09:28 AM

May help a little but I would suggest using some sort of foam for the backing instead of coroplast. Most of the styrofoams have at least some sort of insulative properties which would help keep the heat in and the cold out. Generally range in the R5 value per inch of thickness IIRC.
I have actually done something similar this winter except my reflectors are on the outside of the house. I purchased a roll of fiber infused aluminum attic insulation sheeting and cover the old extra 4x8 sheet of coroplast I had laying around with it. Then I went and bought four, 1/2" thick, 4x8 sheets of aluminum coated styrofoam boards. Being retired I have a little time to play with them throughout the day so I rearrange them in my back yard to reflect the sun into the house as needed. At this time of year I only get about three hours of useful sun a day as a neighbor's tree blocks the good sun for over an hour right around noon.
As far as Mylar goes, it is more reflective but depending on the quality of the foil only by a few percent. Also I've read that Mylar tends to scratch easily which may affect its reflectivity a bit. Sounds like a fun little project. Have fun.

JJ

jjackstone · 01-11-17, 09:32 AM

Ha! So funny. Nate posted a few minutes before me. The Lowes link he provides are the exact styro boards I mentioned. They have aluminum foil as opposed to Mylar as a reflective surface. And the surface is not smooth so there is a little loss there too. But at eight bucks a sheet it was worth it.
JJ

natethebrown · 01-11-17, 09:39 AM

Quote:

Originally Posted by jjackstone

They have aluminum foil as opposed to Mylar as a reflective surface. And the surface is not smooth so there is a little loss there too. But at eight bucks a sheet it was worth it.
JJ

The foam that I put a link up of is not aluminum foil backed because it can very easily be melted with a hot knife (I should know, the wifey had me do a crafty project a couple of months ago). They probably do sell aluminum backed foam which might be what you are thinking of.

jjackstone · 01-11-17, 11:34 AM

You're right. I have the R-Tech. Not the polyshield.
JJ

CrankyDoug · 01-20-17, 07:47 PM

I ended up using 3/4" XPS (pink board) due to its rigidity. For windows I want to insulate I cut a piece that is slightly snug in the window frame. A one inch hole at one end makes a good pulling point for removing it from the frame. This provides insulation and also stops air convection, which I think is the greater problem with windows.

I also made a few of these to plug the roof vent skylights on my RV.

The XPS doesn't fall apart from repeated handling like the foil faced foam boards I have used. And you can always glue some foil to one face of the XPS after peeling the poly film.

01-10-17, 04:02 PM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Aluminum foil reflectivity I was thinking about Aluminum foil reflectivity, after I noticed that I could feel heat on my face from the foil coated insulated foam. I knew the foil wasn't warm, but I could feel heat from it.. It took a few seconds to realize that 'heat' was radiating from my face.. It was bouncing back from the mirror effect of the foil.. Then, I googled and found some stuff that's even more reflective! Mylar Reflective Film! https://www.amazon.com/VIVOSUN-Horti.../dp/B018VI77QW So, as I sit here in this small room, with two windows next to me, I'm wondering if the heat from my body, wifi router and computer system, is radiating towards that cold window, and escaping from this little room?? Does the warm air moving around inside this room emit IR radiation? And would that emitted radiation be reflected back into the room, by Mylar foil? The idea is to cover the windows at night, with a sheet of coroplast, with a coating of Mylar reflective film, to reflect heat away from the windows. (It would also keep air-flow on the windows lower).. I've heard those Space Blankets https://en.wikipedia.org/wiki/Space_blanket actually work pretty well.. And, I could turn the Coroplast-Mylar around backwards on hot sunny days.. Keeping my little computer room cooler in the summer.. Your comments please! __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

01-11-17, 09:17 AM	#2
natethebrown Apprentice EcoRenovator Join Date: Aug 2012 Location: North Alabama Posts: 167 Thanks: 0 Thanked 40 Times in 20 Posts	Thermal radiation is a function of temperature. https://en.wikipedia.org/wiki/Stefan...3Boltzmann_law You probably did experience some heating from the radiation reflecting back at you. Those mylar "blankets" they give marathon runners after the race do work...to an extent. Once the mylar touches the skin, you can feel that it isn't helping you keep that warm because thermal conductivity & thermal convection sucks the heat away quicker. For your window, your absolute best value would be to insulate it with insulation to dramatically decrease both conduction and convection. I believe these foam boards even have the Mylar film on them: https://www.lowes.com/pd/Expanded-Po...875-ft/3365568

01-11-17, 09:28 AM	#3
jjackstone Helper EcoRenovator Join Date: Mar 2009 Location: Sacramento,Ca Posts: 88 Thanks: 5 Thanked 32 Times in 23 Posts	May help a little but I would suggest using some sort of foam for the backing instead of coroplast. Most of the styrofoams have at least some sort of insulative properties which would help keep the heat in and the cold out. Generally range in the R5 value per inch of thickness IIRC. I have actually done something similar this winter except my reflectors are on the outside of the house. I purchased a roll of fiber infused aluminum attic insulation sheeting and cover the old extra 4x8 sheet of coroplast I had laying around with it. Then I went and bought four, 1/2" thick, 4x8 sheets of aluminum coated styrofoam boards. Being retired I have a little time to play with them throughout the day so I rearrange them in my back yard to reflect the sun into the house as needed. At this time of year I only get about three hours of useful sun a day as a neighbor's tree blocks the good sun for over an hour right around noon. As far as Mylar goes, it is more reflective but depending on the quality of the foil only by a few percent. Also I've read that Mylar tends to scratch easily which may affect its reflectivity a bit. Sounds like a fun little project. Have fun. JJ

01-11-17, 09:32 AM	#4
jjackstone Helper EcoRenovator Join Date: Mar 2009 Location: Sacramento,Ca Posts: 88 Thanks: 5 Thanked 32 Times in 23 Posts	Ha! So funny. Nate posted a few minutes before me. The Lowes link he provides are the exact styro boards I mentioned. They have aluminum foil as opposed to Mylar as a reflective surface. And the surface is not smooth so there is a little loss there too. But at eight bucks a sheet it was worth it. JJ

01-11-17, 11:34 AM	#6
jjackstone Helper EcoRenovator Join Date: Mar 2009 Location: Sacramento,Ca Posts: 88 Thanks: 5 Thanked 32 Times in 23 Posts	You're right. I have the R-Tech. Not the polyshield. JJ

01-20-17, 07:47 PM	#7
CrankyDoug Apprentice EcoRenovator Join Date: Jul 2016 Location: Georgia Posts: 100 Thanks: 6 Thanked 14 Times in 11 Posts	I ended up using 3/4" XPS (pink board) due to its rigidity. For windows I want to insulate I cut a piece that is slightly snug in the window frame. A one inch hole at one end makes a good pulling point for removing it from the frame. This provides insulation and also stops air convection, which I think is the greater problem with windows. I also made a few of these to plug the roof vent skylights on my RV. The XPS doesn't fall apart from repeated handling like the foil faced foam boards I have used. And you can always glue some foil to one face of the XPS after peeling the poly film.