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My family will buy a car, so to minimise the car's air conditioning and heating (and thus fuel) costs, how should we choose a car exterior's colour and the interior's colour and material (eg fabric vs leather)?

For example, if my aunt lives in Toronto, Canada, which is cold from Sep to May (9 months), then does it make sense to choose a darker colour which apparently absorbs more heat? Sadly, I know no physics so don't understand https://physics.stackexchange.com/a/96581/53143.

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    For the best thermal isolation, i.e. stays cool in the summer sun and warm in the winter, you want light colors. Another thing to note is that keeping the car covered at night will keep it substantially warmer. A garage is best but even just some kind of little roof over the car will keep it much warmer. This is because the cover prevents heat radiating out into the night sky. – DanielSank Dec 17 '14 at 06:38
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    Fabric and physical car designs (such as window placements, sunroofs, etc) are also factors. Make sure you take those into consideration as well, and they'll probably have a significantly higher weight to your question. – Ethan Allen Dec 17 '14 at 06:41
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    Mythbusters tested it see http://en.wikipedia.org/wiki/MythBusters_(2005_season)#Biscuit_Bazooka_Spinoff – pentane Dec 17 '14 at 13:24
  • @CarlWitthoft I had intended my last sentence to differentiate this, so did it help answer why this doesn't duplicate? –  Dec 17 '14 at 14:43
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    No, failure to understand does not constitute nonduplication – Carl Witthoft Dec 17 '14 at 14:58
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    @CarlWitthoft Where should I ask for extra clarificatin then? –  Dec 17 '14 at 15:29
  • @DanielSank By what mechanism would a white car stay warmer in winter? – endolith Apr 26 '18 at 19:08
  • @endolith depends on the circumstances. If the car is warmer than the outside, e.g. because you used it with the heat on, and you then turn it off and leave it to sit somewhere not in the sun, then the white car will stay warmer for reasons explained here. – DanielSank Apr 26 '18 at 20:05
  • @DanielSank A paint's behavior in the visible spectrum doesn't imply much about its behavior in the infrared. Cars are irradiated by visible light, but don't emit it (unless they're on fire). – endolith Apr 26 '18 at 20:32
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    @endolith Yes, a car absorbs visible light and emits mostly infrared. This is sensible: the sun is not in equilibrium with the Earth, so the sun irradiates an object, but that object is cooler than the sun, so the object re-emits with a different spectrum that is mostly infrared. Still, the car needs to absorb visible sunlight in the first place in order to heat up. Ah now I see your point: once the car is out of the sun, the thermal radiation won't have much to do with the paint's optical color. Good point. – DanielSank Apr 26 '18 at 20:52

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Okay, so first:

Light can be [is] broken down into a spectrum ranging from shortwave lengths to long wave-lenghs. Visible light (the part of the spectrum we humans can see) contains the colours which are all around us. An objects colour directly relates to which wavelength(s) of light it reflects.

White cars are best at refracting light as it reflects every colour in the visible spectrum (white light [like sunlight] being made from all the colours combined); black on the other hand doesn't reflect any colour light which hits it at all. Since non-reflected light is absorbed into an object (in the cars case here) it can be converted into heat energy, warming the cars interior.

So the best colour car to get (to keep the interior cool) would be a hue which reflects the most sunlight (or absorbs the least depending on which way you look at it) of which would be white or silver in highly reflective/glossy sheen.

To make the interior of a vehicle warmer in climates which don't boast high temperatures all year round though, a colour such as yellow or grey in a non-metalic/shiny sheen is a good option- these colours aren't full extremes of black or white and so adequately reflect light whilst also absorb a fair amount too helping maintain a good temperature inside the car. Having a non reflective paint means less light is refracted and so more is absorbed into the vehicle- making it easier to warm up with less sun.

Interior fabrics/leathers mostly absorb heat and so the same principal applies: the darker the stuff, the hotter it will get. White interiors do heat up fast too if they are in constant sunlight with no way of getting cool (such as an open window or A/C. So putting your car undercover when parked or having one of those thingys which goes over the windscreen is a good idea in any situation.

A cars paint job though isn't really the biggest dictator on how hot a car will get- though it does place a good part; things such as windows, their tinting, other inner materials [plastics or metals] and the cars body itself also are factors in how much a car is heated and how fast, so all of these need to be taken into account before buying- as well as the overall appeal of the vehicle and whether it can fit anything bigger than a fat guinea pig inside...

Harry David
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  • Oh, and yes- so a cars colour does reflect on how hot it gets too also it's cost in some cases :) – Harry David Dec 17 '14 at 11:30
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    Thank you, but I just want to clarify. You wrote that the best colour car to get for a car would be a hue which reflects the most sunlight (or absorbs the least ...), but I exemplified with Toronto, which usually has 9 months of cold weather, so I'd want the car to be warm? I admit that the car would be too warm in the summer, but I thought that this disadvantage would be outweighed by the more frequent cold weather. So why NOT a dark colour? Or did you mean that even with Toronto's coldness, a light colour is better? Why? –  Dec 17 '14 at 13:35
  • Will you please to respond in your answer, and not as a comment? –  Dec 17 '14 at 13:35
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    Blatantly weak answer: "white" often is not at all reflective in the IR, for example. The overriding cause of hot interiors is large amounts of glass, which transmit visible light but reflect the re-emitted internal IR wavelengths. – Carl Witthoft Dec 17 '14 at 14:35
  • don't be so meticulous about the effect of light on the temperature. just buy a one with better air conditioners... ;) that's my opinion and i do the same for myself... – P.A.M Dec 17 '14 at 21:26
  • @CarlWitthoft, Ha! It be blatantly stronger than your answer to this question what-say... :P – Harry David Sep 17 '15 at 09:55