Foldy is a folded, aerodynamic piece of paper (shaped like a pentagon!) who can glide on currents of air. How does she do it? It's the magic of 3 × 4 dimensions and intricate folds (which Fries can't seem to grasp)! Despite her pleasant appearance, Foldy often holds on to grudges.
That said, Stapy is Foldy's best and dearest friend. Their bond might be stronger than any two characters in the show. They fight for and stand up for one another. So sweet (yes, they like eachother, so what?)!