Molecular structure as shown in the figure, is the natural rubber. Contain carbon (blue sphere) and hydrogen (red sphere) Adherence by covalent bond. A polymer is linear or reticulate. The molecules to a coil winding band. The van der Waals adhesion between polymer chain together. While being stretched. Molecular coil winding circle and twisted to change shape is quite straight. Make the length of rubber, many changes. When the stretching force from outside is gone. Polymer chain will vibrate with heat and shrink back to its original state.