Photonic crystal fibers (PCFs) have been receiving increasing attention over the past few years. They are single material fibers that use an array of air holes in the cladding to confine light to a core, instead of the more usual refractive index step within the solid material of a conventional fiber. As PCFs become more well-understood mainstream structures, the need arises to develop techniques to process them post-fabrication to form all-fiber devices. We have chosen to study heat-treatment processes analogous to the tapering of conventional fibers, except that in PCFs there is a second degree of freedom to exploit. Not only can the fiber be stretched to locally reduce its cross-sectional area, the air holes can be changed in size by heating alone under the effect of surface tension.