Mechanical and thermal property values of carbon fiber-reinforced polymer (CFRP) composites are readily available. However, the small diameter and thermal anisotropy of the carbon filaments pose significant challenges for measuring thermal diffusivity of the constituent fibers. As a result, the literature describes many techniques to address this issue. Here, a new method for the direct, bulk measurement of on-axis thermal diffusivity of a matrix-free carbon fiber bundle is reported. Aligned carbon fiber tows were uniformly compacted into a collimated, cylindrical bundles using heat-shrink tubing, and fixed such that the fibers remained unwetted, in the center of an epoxy disk, which was subsequently analyzed for thermal diffusivity using laser flash analysis.