Parafilm "M" is a plastic film, malleable and stretchable. It is for single use.
It is delivered in a cardboard box, as a roll, and covered on one side with a very thin plastic film, to remove (and discard) before using the parafilm.
Parafilm "M" is essential in a chemistry laboratory. It is used to cover and close various containers (beakers, Erlenmeyer flasks, volumetric flasks), to partially protect them (but not hermetically). It must be stretched before being applied to the opening of the container to be closed.