well my title is my question; how do i make a invisble barrier? but i have another question in mind. can ai go through the barrier?

Put a lot of crates, and replace their shaders.

Thats a stupid way to do it.

Just make a Box around the map and make it so there is no texture and it is solid. Thats all you need to do.

wait iTails i didnt understand that.
so would it work if i made a wall and add a +sky texture thing?
but dont add collision geometry?
sorry its just i want a invisble barrier about the width of bloodgulch. from flamethrower to plasma cannon not base to base.

You make a Box "Around" [not in] the map so that the projectiles can't go out either. You make it a collision geometry. You just make it have a Transparent Texture, or no texture at all, I think.

You could use player clipping. There is a tutorial on how to use it in the Official HEK Tutorial. Also, AI couldn't go through it.

You can also make a box and place it where ever in your map. Then give it the material +sky and attach it to your frame.

Playerclipping is the best for invivisble walls.
To make it, use a shader called "+Unused" and then the playerclipping sumbol. Sorry, forget what it is.

You can shoot through it, but can't go though it. I don't know about AI.

If they can't go through it was well, you could try making trigger volumes that detect you leaving the area and prevent you from going foreward. There's also a cieling player clip setting in the maps tag, but that only prevents vehivles from going too high.

It makes it so you don't crash into an invisible wall. You fly up then it pushes you down without any collision.