Prefold diapers are rectangle pieces of fabric that are divided lengthwise into three sections. They have more layers in the middle and fewer layers on the sides as opposed to flat diapers which are the same thickness throughout. Prefolds require fastening with pins or a snappi (plastic fastening mechanism used instead of pins) and need a waterproof cover. They are very versatile being also used as pocket diaper inserts for extra absorbency, doublers, burpcloths and eventually recycled as house rags!
Fitted diapers have a contoured shape and have elastics or gathered edges around the legs and back making them easier to use than prefolds. They fastened with either aplix (Velcro) or snaps and require a waterproof cover.