Pea Pods have a graduated sizing system to ensure a perfect fit at every stage of baby's development. 1. Adjust nappy to suit baby's age/weight range... The internal leg elastic adjusts like a bra strap! No need to re-adjust until baby grows.2. Snap bamboo absorber into place with stay-dry panel against baby's skin (can also be used "pocket style").3. Fit to baby. Night time: add a night booster. This will give Pea Pods an added boost for overnight or extended periods of time for up to 12 hours.