This also creates a pressure difference that causes the vapor to flow towards the cooler end of the tube. This process is capable of transporting heat from a hot region to a colder region. It requires no addition of external energy and can be manufactured to have any geometry or property desired. Most heat pipes currently used have copper, stainless steel, or aluminum casings. The wick is often a woven wire mesh that is composed of very small pores.
Stainless steel is easiest to work with but copper is also used.
The pore size is important because the wick operates under the principle of capillary action. Capillary action describes how fluid in a very small tube will be forced up through this tiny opening causing the fluid to rise. The wick is usually located against the inside walls of the heat pipe and can have various geometries as seen here. To determine the appropriate working fluid, there are several considerations to be weighed. The vaporization and condensation point of the fluid, in addition to its operating temperature and its latent heat of vaporization.