Dreaming substance refers to the immersive environment that shapes the world of images in which our bodies inhabit. The term arises from the desire to complicate the simplistic ontological distribution we have received from the Cartesian tradition: apart from res cogitans, thinking substance, and res extensa, extended substance occupying material space, we propose a third substance: res somnians, or dreaming substance, composed of different images that have no material support outside the body, entities that are light and unrecognised by the hegemonic modern colonial tradition, but truly seismic in their impact.