[T2] I hate electrical problems-now color of tarps vs heat reflected

[Mike Benthin]

We have to differentiate here between reflection, insolation and 
absorption/conduction.  The more that is reflected, the less gets 
through by either insolation or conduction.  Insolation is getting 
through infrared light waves that then heat what they hit, vs blocking 
that by being thicker.  Color is a factor in reducing 
absorption/Conduction, where more is absorbed by grey than white-note 
how your black seats are hotter than the white ones!
    With a tarp we must factor in heat by radiation that directly gets 
through due to thinness/transparency/porosity (why a white t-shirt has a 
low spf) vs CONDUCTION  that heats a thicker surface more when 
gray/silver vs white and getting the underside  hot and then heating the 
air beneath it.  Indeed, if thin, a blue tarp may make you feel hotter 
than the thicker silver one if it lets more insolation through and its 
darker color allows more conduction.
    Instead of screening a home window or  a skylight, I cover it with 
an inch thick layer of thermax foam, which stops both insolation and 
conduction (but leaves it dark).  Shades inside our bus windows do 
little to stop the insolation through the glass that then heats the air 
and curtain.  For such windows it is best to cover from the outside, 
such as using a 90% light blocking solar screening that is put on the 
outside (we use magnets on the screen edge).  RVers swear by Reflectix, 
which is a mirrorlike reflective plastic bonded to an airlayer and 
another layer of mirror- keeps it warmer in winter and blocks/reflects 
solar rays in summer.  Maybe if right agaist the glass inside, but many 
have "fried" their window seals from the heat buildup just under the 
glass. It is very useful in covering the windshield.

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