I might agree with the "black side down" theory if the bladder were on a stable flat
surface (i.e. parked in a camp ground).  But I/we (when traveling) rarely stay put
for an entire day and, on the types of roads I drive (and maybe even your
interstate),  the bladder gets sloshed around so much that I think it does not
matter much which side is up or down.  Also from my desert experience, water in a
rigid dark colour plastic gerry can will heat up to bath temp on a 40+ C day in
direct sunlight.  Keeping the water at bath temp is a function of the outside
ambient temp.  Here in Egypt, in the "winter", by the time we stop driving at 4:30
(sunset is at 5:30) and by that time the outside temp has cooled off to about 5 C
and the heat is sucked out of anything real fast, that is why we had to add boiling
water to the "Solar Shower" to make it pleasurable.  Also in "winter" here, with the
"Solar Shower" in the luggage rack and driving, the 20 C wind keeps sucking the heat
out of the "Solar Shower" so the temp in "Solar Shower"  bag struggles to get over
20C.  Summer experience will differ, but even then, at night, things cool off real
fast.  Showering at noon is a bit too conspicuous.  Malcolm

Doug Alcock wrote:

> Ahhhh ---- so I'm completely and utterly wrong (and glad to know it). I'll be
> flipping my shower over right smartly. Thanks. I wonder which way Malcolm is
> turning his shower over there in Egypt.........   Cheers,   Doug