Abstract: Drawn polymer fibers have internal channels running, at least partially, through the length of the fibers. These fibers may be configured to for use as thermal isolators that can thermally isolate material at the central core of the fiber from the outside environment. In such instances, the channels may be used as insulating channels and/or a heating or cooling fluid can be pumped through the channels to maintain the temperature of the material at the inner core. As another application, the fibers may be used as recuperative, regenerative, parallel-flow, counter-flow, cross-flow or condenser/evaporator heat exchangers. In this case, the channels may be used to direct fluid flow. The fiber may allow for the exchange of heat between fluids in the channels.