A thermal insulator is a material that does not conduct heat well, i.e., has a relatively low thermal conductivity (see thermal conduction). Plastics, wood, cork, and some fabrics are good thermal insulators. The reason is that they contain weak molecular bonds in disorderly arrangements. Heat is transfered in a material by the vibration of the atoms and molecules. A disorderly arrangement of particles and bonds slows down the passage of heat through the material. Compare with thermal conductor.