For nearly half a century textile prostheses have been intensively used in vascular surgery. They have saved millions of human lives, but they are not yet perfect. Graft failures have been, in part, attributed to the prostheses finishing processes, generally based on thermal treatments. These treatments permit to reduce fabric porosity and fix the wavy form of prosthetic tube walls involved by crimping process. Four tubular fabrics have been woven with different polyethylene terephthalate (PET) yarns spun under different industrial processes: Setila, Dacron, Diolen and Viscosuisse. Three heat setting techniques were investigated for prostheses crimping: dry heat, vapor heat and autoclaving. Crystallinity index and crystal growth in the equatorial directions have been calculated from Wide Angle X-ray Scattering scans. The aim was to analyze physical structural changes of PET fibers after thermal finishing processes applied to textile vascular prostheses and highlight fiber morphological evolutions related to these treatments. Viscosuisse yarns held the largest crystalline domains built up of numerous crystals but smaller than Dacron ones. However, the best crystalline configurations for the overall yarns were generally obtained for dry heat processes. Compromise regions of treatment conditions for prosthetic Dacron tubes were also obtained to optimize crystal development for the different crimping processes.