Tim Mitchell wrote in message ...
In article , Alex
writes
normally 24mm foamcore or even 28mm is used for this purpose though the
later is less usual.,if you can find some company that will cut it to size
for you expect to pay £20.00 for 600 x 600 mm

This isn't very secure though, our neighbour had a break-in with a panel
like this. They just pushed it through the frame.
If it's only the beads holding it in, I guess you could push a glazed panel
through the frame too.