What is soul made up of?

I was just reading about the Hindu concepts of Atman and Paramatman and this question hit me. In some philosophies of Hinduism, like Dvaita, there is a distinction between Atman (the individual soul) and Paramatman (the Supreme soul). In that case, the Atman is what manifests as us, people, by taking a body. They say that this atman is trapped inside the body and is waiting to be liberated (called Moksha). Now my question is what is this atman made up of? They say its not physical. Its not the mind either. Then how is it trapped inside a physical body? How can something non-physical be trapped inside a physical body? What is it then made up of?