A functional item of clothing worn as an undergarment by infants and toddlers to keep crap and piss contained until the garment can be thrown away or washed.
The internal, absorbant part of a disposable diaper usually consists of a type of wood cellulose fiber, and polyacrylate. The external part of the diaper is made of polypropylene, polyester, and polyethylene. (Notice they're all synthetic.) The straps are usually made of synthetic rubber.
The polyacrylate absorbents inside the diaper can also turn liquid into a sort of gel.