What's the difference between thermoset plastics and thermoplastics?

Cross-linking a high-level 101 of the injection molding manufacturing process: Basics of Injection Molding

Thermoplastics and thermoset plastics are commonly used in injection molding, and each of the two have their own unique advantages.

What’s the Difference?

  1. Thermoset Plastics: Linked by covalent bonds; undergo curing process during heating and shaping which causes permanent chemical change in molecular structure. Common materials include epoxy, silicone, polyurethane.

    (TLDR; material remains in a permanent solid state after being cured once).

  2. Thermoplastics: Linked by Van der Waals bonds; can be heated and reheated, reversible plastic operation



  • Advantages

    • Commonly used for aesthetic surface finishes
    • Recylability, end plastic part can be re-melted and formed into different shapes (commonly ued for toys, furniture, etc.)
  • Disadvantages

    • Ineffective for parts regularly exposed to extreme heat or rapidly varying temperature ranges as they can melt more easily
    • Molding process requires higher heat and pressure to create parts

Thermoset Plastics

  • Advantages

    • Generally do not melt when exposed to heat
    • Do not deform, warp, or lose shape in varying temp. ranges
    • Molding process is cheaper as they require less complex tooling (i.e. far less heat and pressure)
  • Disadvantages

    • Much more difficult to surface finish
    • Cannot be remolded or reshaped
    • Poor thermal conductivity and rigidity