Four parts are included in a bandaid.
Contains a top layer a wound pad an adhesive and a protective film on top of the adhesive.
The only part that has changed significantly over time is the material used for the top layer.
The top layer was traditionally made from cotton or rayon fabric (which is derived from wood) with an adhesive applied to the underside.
In recent years band-aids have become waterproof if not moisture resistant and so are made from plastic.
Additionally they are breathable which speeds up the healing process.