I'm going to change my thinking on this a bit and explain as well.

If you go to a thermal engineering book and lookup emissivity and
absorption then I think you will find the mirror/polished has the lowest
values which drove my original thinking.

On the sunny side with a mirror finnish you have a low absorption. The
problem with the rest of the equation is that you have low emissivity as
well, so what heat is absorbed is very poorly radiated. This low
radient level (low emissivity) causes the surface temperature of the
aluminum to be quite high. Where this looses ultimately against a white
painted surface is that you then have a high temperature surface that is
conducting with either your hand (if you touch it) as well as the air
inside the trailer so the trailer may ultimately be hotter with the
polished finish.

Go with a cheap white paint.



Bill Daniels wrote:
"Udo Rumpf" wrote in message
.. .

I agree that the most highly polished Alu
has nothing against a pure white paint when it comes the reflectivity and
absorption rates of sun light. I just do not know where this myth comes
from.
Udo


Clear reflective metal absorbs less heat than any paint, even white.

A club member painted his bare aluminum tube type trailer white and noted
that the decrease in heat buildup was very noticeable. Apparently, YMMV.

Tony V "6N"


I have to agree with Udo.

Anyone who has lived in the desert knows that polished aluminum will get hot
enough to inflict burns if left out in the sun. Painted white surfaces
won't.

The best evidence I know of for this is the telescopes at the National Solar
Observatory at Sunspot, NM. They are painted "Telescope White" to prevent
solar heating from distorting the supporting structure. If polished
aluminum worked better, that's what they would use.

The only rational reason for polishing a trailer instead of painting it
weight. Polishing is lighter than paint and that may save a little fuel.

Painting aluminum is a tiny bit involved but not difficult. Prepping the
surface with an etching wash and then using a good primer is the key -
consult with your paint supplier. Using a roller to paint a trailer is
perfectly reasonable.

Bill Daniels