Diapers that don’t already have a water resistant outer layer, like prefolds, flats, and fitteds, will need a diaper cover over them to keep baby’s clothes (and everything else!) dry. In general, we recommend one diaper cover for every 4-6 diapers in your stash. Most families find that they can reuse a diaper cover a few times before needing to fully wash it; If it is simply damp on the inside you can wipe it down or give it a quick rinse in the sink and then air dry (most covers air dry in a couple of hours). So, take off a diaper cover and wipe down as needed, air it out, and then reuse it at a future diaper change. Polyester diaper waterproof covers are the most common (as in fleece and PUL- polyuretheine laminate) and can be machine washed and dried with the diapers.