I bought Mohu Releaf cardboard antenna. It works much better outside than inside. Mohu explicitly advises against outdoor use of its indoor models, yet I wrapped it in a plastic bag and hung it out of window. It looks a bit shabby so I am looking for ways to improve both the look and protection against elements.
I tried placing antenna between window glasses yet it gets less channels than outside. I have a big outside antenna, again it gets less channels.
Dimensions: 9″ x 11.5″
Effect of elements on Leaf antennas
http://mohu.freshdesk.com/support/solutions/articles/4000026474-can-i-use-my-leaf-curve-antenna-outside-or-in-an-attic-
Releaf model
https://releaf.gomohu.com/#specs
Update. I used it in a plastic bag to reduce deterioration yet eventually bought Winegard Elite on a sale, now have a few channels more. May be will use the leaf with bedroom television.
Best Answer
At the risk that it might alter the properties of the cardboard in some way that might matter at radio-frequencies, I'd slather it in epoxy resin for waterproofing and follow up with a coat or two of spar varnish for UV protection.