Why the face dries long before the core does
A cushion is not one material. There is a face fabric, usually a backing or scrim behind it, then a foam or fibre core that can be several inches thick, and on many pieces a sealed inner casing around that core. Water moves into all of those layers during cleaning but only evaporates from the outer surface. That is why a sofa can feel dry to the hand within two hours while the middle of the cushion is still holding moisture. Sitting on a piece in that state pushes the remaining water back to the surface and leaves a damp patch, which is the most common reason people think a cleaning has failed.