For some years now I've used crown boards (inner roofs) made from a
sheet of transparent plastic.  I use anything I can lay my hands on,
providing it's sufficiently rigid not to sag too much.  (I think mostly
it's acrylic or polycarbonate.)  Providing your hives use top bee space,
you don't need any fancy edging to the sheets - just cut them to size
and use them.
 
You can usually see the bees just by taking off the roof and looking
through the plastic.  Sometimes, if the cluster is very low down, a
torch is useful.  Shine it down between the frames.  If all's well you
should be able to see some movement, even in very cold weather.
 
The only potential problem I can think of is that there may be a greater
tendency to condensation under certain climatic conditions.  I just prop
the corners of the sheet up by about a millimeter or two with some
matchsticks and this seems to be sufficient for the conditions in
SE England.
 
--
Malcolm Roe                                Phone  :  +44 1442 345104
Crosfield Electronics Ltd                  Fax    :  +44 1442 232301
Hemel Hempstead, Herts. HP2 7RH, UK        E-mail :  [log in to unmask]
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