Why are earbud wires for an mp3 player coated with plastic
1, to better conduct the sound
2, to insulate the wires
3, so they look good
4, so they dont break

The naked wires are dangerous, so the plastic coating insulates and protects the wires :)

Texture and composition are different because they are not the same aspect. texture has to do with feel and so on, where as composition is the chemical makeup which you cant touch like you can texture.