Solid at room temperature that can be melted and softened by heating, placed into a mold or other shaping device, and then cooled to give the desired shape
When placed into a mold and then heated, they initially drop in viscosity (liquify) but then cure (harden) upon further heating, thus giving the desired shape and solid properties
After curing, if thermosets are reheated, they will soften somewhat but do not melt and therefore cannot be reshaped