Cat flaps

Our two are in and out constantly all day, there's no way I'd want to be without one. They also get chased a lot by neighbouring cats, so we have a microchip one so they can safely run inside if they need to. We have our cat flap in our large bifold double glazed doors.

Our cat flap is installed in a glass door. The door is double-glazed - the guy who installed the flap was from a double-glazing firm.

I've always had cats as a child and an adult and never had a cat flap. No issues.

It's possible to put cat flaps in glass or even through walls.
My friend has a tunnel through a wall (they had an extension built, builders also put this in) with a flap. The cats have got used to it!
If you had a window at a suitable height maybe you could have one there?
Not sure I would want to put a flap in expensive bifold doors!
My neighbour has cats but no flap, whiiis ok. She opens a window when they're in for the cats to use but if she goes out the cats are either in or out.
Personally I'm not keen on that as I think it's safer for your cats to be able to get in at any time.

We also have a cat flap in a double glazed door. DSis has one in her kitchen wall - it a little tunnel, with the flap bit on the outside.

We couldn't do without one. DCat is in and out all day and night.

We have ours in the front door as our back door is a sliding glass one. We are not on a busy street so the front one suits us

Get dh to be in charge of letting the cat in and out, he’ll soon put a flap in.

I did similar to get a dishwasher.

No cat flap here.
She miaows to go out, I open the door. She miaows to come in, I open the door. It's never been a problem.

we don't, so that we don't get a load of mice in the house. There's a cat flap into the garage where they have a bed but they ask at the door in te house (which obviously means we have to have a litter tray)