There is a product specifically designed to address the heat problem without
to much tint.
It's called Foliatec and is distributed by Stricty Foreign in Allentown,PA.
I was told that Strictly Foriegn is the US dealer and their number is
610.391.1902 if you're interested.
BE WARNED: this stuff is really pricey!

A quote from the pamplet I have:
"With intense sunhine, Chromolux takes on a restrained metallic gloss, and
despite high light transparency, up to 58% of the heat is diverted. If on
the otherhand, the sky is cloudy, the degree of transparency is redued to a
light shading."

They have a display at  Stricty Foreign with a glass wheel tinted half and
half. Over the glass is a heat lamp. Its stops a lot of heat and is very
lightly coated.  Karl B could stop by Stricty Foreign and put his hand under
the display and vouch for the marked difference in temp.
They have a website http://www.foliatec.com

It really isnt very dark and I was entertaining the idea of double layers to
get the heat control and desired tint. Haven't done it yet though!

Cheers,
Dave C.
Williamsburg, VA
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'85 GL Westy (His)
'91 Cabriolet (Hers)