Thermoset material can only be heated and shaped once. If re-heated they cannot soften as polymer chains are interlinked, Separate polymers are joined in order to form a huge polymer. The main thermosetting materials are epoxy resin, formaldehyde, bakelite and Phenol resin (Phenol formaldehyde).
Thermoplastics can be heated and shaped may times. Thermoplastics will soften when it is heated and can be shaped when hot. The plastic will harden when cooled, but can be reshaped because their is no links between the polymers chains. Some common thermoplastics are Nylon (polyamide), PVC (polyvinyl chloride), polystyrene, polypropylene.