Value of the data •The WAXD patterns highlight the highly-oriented non-crystalline mesophases in amorphous and semi-crystalline polymers. •The data shows the reversibility behaviour of the mesophase in P3HB under cyclic tensile loading. •This data can be compared to other WAXD and SAXS measurements from other P3HB fibers and films. •The data is of high interest to the field of bio-polymers and is potentially useful for the further development of melt-spinning of P3HB fibers. •The detailed description of WAXD and anisotropic 2D SAXS pattern data analysis of melt-spun fibers is potentially useful to many researchers.