Metallic bonding is the cause for many of the properties of metals, such as strength, malleability, ductility, lustre, conduction of heat and electricity.
The sea of electrons and the positive ions in the metal have a strong attractive force between them which is why metals possess high strength.
It is because of the mobile electrons, that metals are good conductors of heat and electricity, as the electrons can move quickly through the body of the metal and pass electricity and heat much faster.