Sounds like a principle similar to a double pane window.  The air gap acts
an insulator.

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Richard Smith
Sent: Thursday, June 11, 2015 11:01 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: how to cool a poptop?

They have mainly disappeared now, but for many years the taxis in Hong
Kong (Toyota Crowns) had a dual roof. On top of the regular roof, and
separated by about an inch, was another roof. The idea was that the flow
of air between the two roofs, as well as the shade, I guess, would make
for a cooler car. Perhaps this was because there was no air conditioning,
or to ease the burden on the air conditioner.