"Janet Baraclough.." wrote in
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The message
from Martin Brown contains these
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If it is the same stuff as I am using (intended for conservatory
roof
applications) it may transmit around 6% less light due to the
internal
structure and being double skinned. But it more than makes up for
that
by providing better insulation. I have known other cacti growers
use
this stuff to great effect in their greenhouses (and intend to do
the
same).

I'd be a bit less convinced by the 6mm grade. I reckon that may
reflect
back as much as 10% of the incident light. But even then it may
not be a
real issue since it is the warmth that encourages early
germination.

In Scotland, conservatory roofs use a triple walled polycarbonate
sheet for higher insulation still. You might find that even better
for
your GH.

I have a funny feeling that that is overkill, but I can't prove it..Do
you know of a source in which the heat transmission properties of twin
and triple walled polycarbonate are compared?

Franz