  Higher efficiency, lower cost refrigeration is needed for both large and
small scale cooling. Refrigerators using entropy changes during cycles of
stretching or hydrostatically compression of a solid are possible alternatives
to the vapor-compression fridges found in homes. We show that high cooling
results from twist changes for twisted, coiled, or supercoiled fibers,
including those of natural rubber, NiTi, and polyethylene fishing line. By
using opposite chiralities of twist and coiling, supercoiled natural rubber
fibers and coiled fishing line fibers result that cool when stretched. A
demonstrated twist-based device for cooling flowing water provides a high
cooling energy and device efficiency. Theory describes the axial and spring
index dependencies of twist-enhanced cooling and its origin in a phase
transformation for polyethylene fibers.
