I really enjoyed the concept of the Immateria in Promethea. It reminded me of the Oversoul by Ralph Waldo Emerson.
The oversoul is about one universal soul that all people share and draw thoughts and knowledge from. The immateria, like the oversoul, is thought and imagination. It is a place that always exists and is transforming in our heads. Our minds contribute to and are our realities. After all, things that we physically experience are only our perceptions of what is going on around us. I think it was best said by Dumbledore in Harry Potter 7. “Of course it is happening inside your head, Harry, but why on earth should that mean that it is not real?" - JK Rowling.
How do we access the immateria? Well, in I <3 Huckabees (the movie), Bernard suggests that Albert break the world down into little pieces. He shows Albert a white sheet and points to one area and tells him that it is NYC. He points to another place, that is Paris, another is Albert himself. The point he was trying to make was that everything is connected. Everyone is connected because every piece of matter is connected to everything else. When Albert finally has the moment when he can see clearly, the images that he physically sees break into little squares and move freely through space. Similar to when Promethea moves into the Immateria, reality morphs into a communal space that all matter can occupy.
There are so many books and films about what is real. I could go on and on, but I'll end it now. I just thought that Promethea answers this question again in a really interesting way.