Polymers are classified by the type and strength of intermolecular forces, which determine physical properties:

Elastomers: Weak intermolecular forces + slight cross-linking. Chains can stretch considerably (500-1000% elongation) and snap back. Glass transition temperature (Tg) well below room temperature. Examples: vulcanized rubber, Buna-S, neoprene, silicone rubber.

Fibers: Strong intermolecular forces (H-bonding, dipole-dipole). High tensile strength, high crystallinity. Can be drawn into long filaments. Tg and Tm both above room temperature. Examples: nylon-6,6 (extensive H-bonding between amide groups), Terylene/Dacron, silk, wool.

Plastics: Intermediate forces. Can be molded under heat and pressure. Divided into thermoplastics (remoldable: PE, PVC, PS) and thermosetting (permanent: Bakelite, melamine).

This classification explains why the same chemical type can have very different applications — rubber (elastomer), nylon (fiber), and Bakelite (thermosetting plastic) all represent different force regimes.