Inside the container is a liquid under its own pressure, that enters the pores of the capillary material, wetting all internal surfaces. Applying heat at any point along the surface of the heat pipe causes the liquid at that point to boil and enter a vapor state. When that happens, the liquid picks up the latent heat of vaporization. The vapor, which then has a higher pressure, moves inside the sealed container to a colder location where it condenses. Thus, the vapor gives up the latent heat of vaporization and moves heat from the input to the output end of the heat pipe.
Heat pipes have an effective thermal conductivity many thousands of times that of copper.
Heat pipes can be built in almost any size and shape. Even though most people perceive it as a simple technology, heat pipe manufacture has been a difficult area to compete in. Simple in concept, but difficult to apply commercially, the heat pipe is a very elusive technology. Any high school student can make a good performing heat pipe with parts from a hardware store. Many early researchers did just that.