Antonyms for the word "folds up" include words like "unfolds," "extends," and "spreads out." When you unfold something, you are reversing the action of folding it up. Similarly, when something extends, it stretches out or expands rather than becoming compact. Another antonym would be "unrolls," which refers to straightening out a rolled-up object. Additionally, "flattens" could be an antonym for folds up if you are referring to something like a piece of paper. Essentially, any action that involves expanding or spreading out an object is an antonym for folding it up.