fitted nappies are entirely absorbent  + typically made from lush  natural fibres like bamboo + organic cotton.

shaped much like a disposable nappy, with gently elasticised legs + waist, they come in a range of fastenings, including snap buttons, hook-and-loop (such as Velcro, Aplix and touchtape) or Snappi fastening.

for waterproofness, fitted nappies require a separate cover

a fitted nappy + a separate cover is an excellent combination for reliable leakproof containment, great for newborn poo-splosions!

some fitted nappies are designed to fit  from birth to toilet training while others are sized to fit a specific weight range. 

the down side to fitted nappies is that they may be more time consuming to put on because of the 2-part system, they are often not as slim fitting as other options and because they are most commonly made from natural fibres, may  take longer to dry.