Thermosets and thermoplastics differ in that thermoplastics can be remelted while thermosets solidify into a crosslinked network during processing. Thermosets offer advantages like low viscosity, electrical insulation, and dimensional stability but also have disadvantages like brittleness and inconsistent properties between batches. Common thermoset materials include phenolics, ureas, unsaturated polyesters, and epoxies which vary in properties like heat resistance, strength, and cost.