A thermoset is a plastic that changes from a liquid to a solid when heat is applied, in the same way that a cake does. They are difficult to recycle as they cannot be melted since the process is irreversible. The process is irreversible as co-valent bonds form between molecules which are very strong so difficult to break. A thermoplastic s a plastic that turns from solid to liquid when heat is applied, and is more like ice. These plastics are recyclable as they can be easily melted down. This process is reversible as intermolecular bonds are between molecules which are easily broken.