De-materializing refers to the process of something becoming less substantial or losing its material form. The antonym for de-materializing is materializing, which describes the process of something becoming more substantial or manifesting in physical form. Other antonyms for de-materializing could include solidifying or concretizing, as these terms describe the process of becoming more tangible or taking on a physical form. Conversely, antonyms for de-materializing may also include etherealizing or spiritualizing, which describe the process of becoming more ethereal or intangible. Ultimately, the antonym for de-materializing depends on the context and the desired outcome of the process at hand.