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Old 04-16-2019, 01:13 PM   #1 (permalink)
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Roof paint for a car? (Repel heat / keep interior cooler)

I did some searching and didn't find much. I wanted to know what difference the particular color of a car makes. Obviously white is the best option for repelling heat, but my geo is a really light red color, and my curiosity was whether a particular color was better than any other (assuming the same...lightness?).

Also during my searching I found someone had brought up painting a car with white elastomeric roof coating as an idea to repel heat, and I wondered if anyone has heard of this.

I usually come up with the weird ideas.

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Old 04-16-2019, 02:22 PM   #2 (permalink)
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You probably won't do better for heat rejection than putting this on your car's roof.

https://www.metrorestyling.com/3M-Chrome-s/366819.htm
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Old 04-16-2019, 02:30 PM   #3 (permalink)
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Quote:
Originally Posted by samwichse View Post
You probably won't do better for heat rejection than putting this on your car's roof.

https://www.metrorestyling.com/3M-Chrome-s/366819.htm
Yes, but it's a first gen metro. If I put that on my roof I'd get run over by someone I blinded within a week.
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Old 04-16-2019, 02:32 PM   #4 (permalink)
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Quote:
Originally Posted by samwichse View Post
You probably won't do better for heat rejection than putting this on your car's roof.

https://www.metrorestyling.com/3M-Chrome-s/366819.htm
That stuff is pricey too! I can get five gallons of the white roof stuff for ~$80 and it would cover my car and my camper (which needs to be done anyway.)
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Old 04-16-2019, 03:19 PM   #5 (permalink)
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There are other options for paint out there. There is stuff that has additives to reflect more heat. I doubt its worth the extra cash looking into it for an automotive application. However, it is interesting stuff.

A quick google search found this company:

https://www.ultimatecoatings.net/

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Old 04-16-2019, 05:02 PM   #6 (permalink)
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So here's what I think I'm going to do.

I need some of this roof coating for my camper anyway, so I'm going to get a bucket of that. Then I'll get some automotive paint in a few colors: I'm thinking red and blue (a light and dark variant of each), black, and white. I'll get some test coupons of some thin aluminum from work, paint each color on one of them, and coat one with the roof stuff. I'll let them sit in the sun for about 3 hours (or until they all reach a steady temperature) and record their resting temp.

Any input on this test? should be some interesting data.

Edit: I will paint ONE color on each coupon.
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Old 04-16-2019, 07:50 PM   #7 (permalink)
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I chrome-wrapped my roof at the end of last summer. The problem with red paint is that it absorbs the higher-frequency (and higher-energy) end of the visible spectrum; that's why on interstate signage, the red part always fades long before the blue does. So, if you want a color other than white or silver, something toward the blue end would probably be best.

I'm not sure how much the chrome wrap is actually doing, but if I can find someone else with a silver Prius this summer it might be fun to leave both of them in the same parking lot and monitor the interior temperatures.
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Old 04-17-2019, 10:59 AM   #8 (permalink)
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Quote:
Originally Posted by Vman455 View Post
I chrome-wrapped my roof at the end of last summer. The problem with red paint is that it absorbs the higher-frequency (and higher-energy) end of the visible spectrum; that's why on interstate signage, the red part always fades long before the blue does. So, if you want a color other than white or silver, something toward the blue end would probably be best.

I'm not sure how much the chrome wrap is actually doing, but if I can find someone else with a silver Prius this summer it might be fun to leave both of them in the same parking lot and monitor the interior temperatures.
Wouldn't blue absorb the red end of the spectrum (including infrared, which equals heat). I understand what you're saying about absorbing the blue end of the spectrum, I deal with UV heating of materials at my job (we use a lot of black canvas and black painted aluminum in our products. The aluminum can reach 200F under a UV light in 5 minutes.)

Maybe the infrared from the sun isn't as large a factor as all the high energy stuff though, I'm not sure (again why I want to do that test.) As it is I may end up just painting the car white myself. After all, it was $350 and already looks ugly.
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Old 04-17-2019, 11:04 AM   #9 (permalink)
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Sound deadeners can have some insulating quality from the heat. That's something I would like to do on my Jeep before this summer.

Well, and because it is loud in my Jeep...
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Old 04-17-2019, 11:35 PM   #10 (permalink)
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When sitting still, heat rejection would mean alot, I guess. But once the car is rolling the aflow of air over the car will cool the roof regardless of color. The benefit of paint therefore is minimal. On your camper, tho... well you hang out in that more often with it stationary, so... makes more sense there.

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