BabyLove Cosifit™ nappies have undergone significant laboratory and home use testing and can last up to 12 hours. However, every child is different in shape and size, so occasionally leakage problems may occur. Other factors, such as how often the child urinates or has a bowel movement may also affect the absorbency of the nappy. The weight range on the pack is a guide only, to help Mums and Dads determine the best size nappy for their child. Sometimes, moving to the next size up will stop leakage issues.