The antonyms for "became soft" are "hardened" and "stiffened". When something becomes soft, it usually loses its rigidity and firmness, making it easier to deform or bend. Oppositely, when something hardens or stiffens, it becomes less pliable and more resistant to change. For instance, a pastry that became soft after baking would harden as it cools down. Similarly, a rubber band that became soft after being stretched for a while would stiffen after being left alone for some time. Using antonyms can help create a more vivid description of an object, process or event and, in turn, enhance the reader's understanding of a text.