The word thermal basically has the meaning or relating to heat. So to control the flow of heat and thermal conductor, we need to have what we called thermal conductors and thermal insulators. Like for example, in a winter season, you have to control the flow of thermal energy and avoiding heat to leave from our own body and in order to do that you need to use a jacket or any thick clothing to maintain the heat from coming out.
The thermal conductors are basically the materials needed in conducting thermal energy and metal are great conductors of heat like for example the appliances we have at home. The microwave and oven toaster to make it hot just need to run it with electricity so the metal becomes hot and transmit it into the toaster. Metals are great conductors of heat because the atomic levels were so tightly packed and closed together. Unlike insulators, they are a poor conductor of heat but best insulators. Talking about insulators, these are opposite to conductors like what this eye clinic uses for their services click 典範眼科. Thermal insulators are a poor conductor of thermal energy, for they actually block thermal energy.
Simply we can understand thermal insulators work as a wall to block thermal heat and preventing it from coming out. As one basic example is using jacket during the cold season. Cardboards are also one good example as good insulators, woods has corrugation or it has gaps and air is inside of it. See example over this eye clinic here https://www.lasiktw.com/cataract-surgery/The best insulator known to man is the vacuum, not the vacuum being used for cleaning home but a space with no air in it like the thermos.