Quote from Habzs on July 29, 2014, 9:13 am

Tie the brush to a func_clip_vphysics, and apply a clip texture. Although it works without having the clip texture, it's always a good practice to apply the texture as it's main purpose is to indicate that there is a clip in place.

Quote from FelixGriffin on July 29, 2014, 11:14 am

Note, however, that a func_clip_vphysics will not block the player. If you want to block everything, you can create a second player clip brush on top of your physics clip one, or just use a func_brush with nodraw or invisible.

Quote from User on July 29, 2014, 1:26 pm

Or just use the invisible texture, (but tie it to a func_detail (or something other), because it splits the visleaves)