These outer shells are the waterproof part of the Pop-In nappy system. As the two parts of the Pop-In system can be separated for washing, you may prefer to alternate the waterproof wraps during the day, rather than washing them after each use. Doing so allows you to purchase less outer shells, and instead air them between uses. They will only need to be washed if soiled or once they start to smell, usually after 2 or 3 uses. The outer shells are only available to purchase separately in the Snowball colour; should you wish to use coloured nappies you will need to purchase the nappies as a complete set of inners and outer shell, either in bamboo or minkee fabrics. We also sell the inner absorbent components of the nappy separately.