Prefolds are pieces of flat cotton (or sometimes hemp) that have been sewn together in such a way that creates more layers in the middle, where more absorbency is needed. So instead of having to fold the fabric to get this effect, these are "pre folded" for you. These are one of the most basic types of diapers (flats probably being THE most basic...we’ll get to those next). They are the most cost efficient and work well. Prefolds need a diaper cover to keep wetness in. It's also recommended to use a fleece diaper liner inside the prefold to keep baby feeling dry.

Flats are like what prefolds start out as. Just a flat piece of absorbent fabric, usually sewn (or "serged") around the edges to keep it from fraying. They can be folded in many different ways to fit the individual needs of each baby. Flats also need a diaper cover to keep wetness in.