I am looking for a solution for my cats wanting to go in and out of the screened in patio through my sliding glass doors during the warm months. I don't want to let the air conditioning out and the heat and humidity in, but my cats love the patio. If I shut the door they will cry out there to come in. I looked on line and all I can find are permanent inserts with a cat flap at the bottom. My hurricane doors are very secure and I don't want to compromise that with an insert that has a cat flap at the bottom. I only need this device in place when I am at home. I am imagining some sort of foot wide thick plastic flap that attaches to the door frame with strong magnets and has a flexible opening at the bottom that the cats can go through when they want. I was even thinking of getting a clear shower curtain, cutting it into a long strip that could attach to the curtain rod at the top and have magnets secure the sides. Does anyone have a solution for sliders that is easy to put up and take down?

Your slider is probably pretty big. For Raiden to access his cat enclosure, my husband bought a piece of thin plexiglass, cut it to the width of the window we were going to use. We had to cut the cat door down because it was supposed to go on a thick door. My husband cut out the opening for the cat door, fastened each side (with glue) to the plexiglass. Now we usually leave the window open with the insert in it. Since Raiden's enclosure is locked and completely covered, we don't have to worry about people getting in there or water getting in anywhere. When we need to go out of town, we remove the insert and close the window. Currently, the window rests on top of the insert. We also put some insulation board around so the air doesn't escape. If your door slides left to right or vice versa, you would need something taller. It needs to be rigid rather than flexible. It would fit into the track and the door frame when the door is open. And you remove it when you don't need it. It could take some creating, but it can be done.

This picture shows the cat door above the steps.

Plexiglass is very light and the thinner ones are somewhat flexible to bend slightly into the track. You wouldn't have that problem if your slider is left to right or right to left and you can butt the slider right up to the plexiglass. You may have to find something to secure it to the slider side. Even duct tape might work okay for the time the panel is up. It's the simplest solution and would solve your problem. The kitty can come and go as it pleases in and out and when you need to close the door for the night or when you're gone, the panel comes out. We bought a fairly large piece of plexiglass and I remember my husband broke the first panel he made! Luckily, we had enough to try again.