2. Pocket doors are used all over the house. Most commonly used in turn-of-the-century homes, they've become more common because of their space-saving construction. Unlike sliding doors, pocket doors actually slide into the wall, rather than along the side of it. 3. Folding doors (usually in a bi-fold form) fold in on either side, and are usually used in closets, laundry rooms, pantries and other small spaces. 4. Flush doors are more contemporary, simple doors smooth on both sides, and generally made of plywood or MDF.