Banners body has a store of extremely high energy particles. When he transforms, they are converted to much lower energy particles and the energy is converted to mass (e=mc^2). When the hulk goes back to banner, is the same process in reverse: mass is converted to much more highly energetic particles.
Banners body has a store of extremely high energy particles. When he transforms, they are converted to much lower energy particles and the energy is converted to mass (e=mc^2). When the hulk goes back to banner, is the same process in reverse: mass is converted to much more highly energetic particles.