One Size One Size Diapers have become the latest rage in cloth diapering. Who doesn’t want the satisfaction of knowing they can buy all the diapers their baby will need in a single purchase!?! We have many customers come into our brick and mortar store to compare our best selling diaper, bumGenius! 4.0 Pocket Diaper, with the Fuzzi Bunz One Size Diaper. Both diapers are built with the same one-size diaper concept; they grow with the baby from birth to potty training.