Folding and stacking objects builds on the concept of a line. The size of the objects can impede performance if they are too big or too little.
Paper to be folded and stacked should be about the size of the standard paper used in printing documents. A piece of paper that is less than 6 inches (15 cm) is apt to be annoying.
Hand towels and wash clothes are a good size, but bath towels are too big. The softness of the fabric is appealing to many people. Sorting by size or colour can be done within ACL 4.0 and above.