I use shade cloth. It lets the air flow through. It only slows water but it stops hail.
http://www.greenhousemegastore.com/...MI3KmGut-_2wIVg8DACh3pLQooEAQYBCABEgLwmPD_BwE
It is also sold at Lowes but I think the linked page is cheaper.
http://www.greenhousemegastore.com/...MI3KmGut-_2wIVg8DACh3pLQooEAQYBCABEgLwmPD_BwE
It is also sold at Lowes but I think the linked page is cheaper.