Here's a breakdown:

* Thermosetting plastics are plastics that undergo a chemical change when heated, forming a rigid, irreversible network structure. They can't be melted and reshaped after this initial curing process. Examples include epoxy resins, polyester resins, and phenolic resins.

* Thermoplastics, on the other hand, are plastics that can be repeatedly melted and reshaped upon heating. They soften when heated and solidify upon cooling. Common examples include polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).

So, thermoplastics are the opposite of thermosetting plastics because they can be repeatedly melted and reshaped, while thermosetting plastics cannot.