I have not heard of a screen window that a cat can't eventually tear. I plan to add hardware cloth to the outside of my windows. It is a fine wire fencing material that you can buy at any home supply store. Cut to fit and staple to the outside. Nail a piece of wood trim on the edges and paint to match. It isn't a fashion statement, so it might be best if used on the back of the house if looks are a concern.

I had my cats get out a couple of weeks ago. Until I get around to doing it to mine, I have to keep the windows closed.