Thirsties Fab Doublers add even more absorption and leak protection without excess bulk. Ideal for heavy wetters and nighttime use. Made from four layers of luxuriously soft cotton velour. Available in 2 sizes for custom fit. When adding to Thirsties Duo Fab Fitted diapers, tuck the doubler into your Thirsties Diaper Cover or Duo Wrap. Wrap and fasten your diaper around baby first and then add the doubler and cover. Or, when using with the Duo Diaper, stuff doubler in the sleeve behind the Duo Diaper insert.