Don’t freak out about your new prefold diapers being huge and flat, they will shrink up and fluff up with washing.
Cotton and hemp: Unbleached cotton has its natural water-resistant coating called cotton oils or cotton wax. In order for them to absorb properly, wash 4-5 times in hot water (120 F/60 C) using proper detergent. Dry on medium between washes to ensure shrinkage and proper absorbency. Prepping diapers is necessary no matter what kind or brand, white or unbleached. Check to see if you diapers are ready by taking a dry diaper to the sink and pouring some water on it. If the water soaks right in, they are ready for use. Wipes and doublers also need this prepping.
Covers: Regular covers should be washed before using, hang to dry or dry on low or medium in the dryer for a short time.
Wool: All wool should be washed and then lanolized before using.
Pocket diapers or diapers with fleece: Wash once prior to use.