Nicki's Diapers Merino Overnight Wool Covers are a great diapering solution for your little one! Lanolizing wool is self-cleaning, and only needs to be washed and lanolized every 3-4 weeks unless soiled.Nicki's Interlock Merino Wool Covers are silky and stretchy. While the overnight design has an increased ability to prevent leaks, the material is still breathable for baby. In addition to overnight use, these diapers are perfect for daytime use since they fit under clothing.