Metal solids contain a positively-charged cation surrounded by a "sea" of delocalised, negatively-charged electrons.
The electrons are able to move freely, and hence transfer kinetic energy throughout the implement at a much quicker rate than non-metals.
Plastic is made of non-metals (Mostly carbon and hydrogen) and therefore is a poor thermal conductor.
Therefore, by coating the metal utensil in plastic, the rate of heat energy transfer to the person in contact's hand is decreased.
