This paper outlines the shrinkage of electrospun polyvinylpyrrolidone (PVP) fiber mats during thermal treatment. The thermal behavior and phase changes within the fibers were investigated by DSC and TGA/DTA. Five precursors with different PVP loading in ethanol were electrospun. The mats shrinkage as function of temperature was measured in the RT-200 degrees C range. Shrinkage rate drastically increased above the polymer glass transition point, T-g (150-180 degrees C), due to increase in polymer chain mobility. Mats shrinkage at 200 degrees C as function of PVP concentration showed a minimum at approximate to 10%wt. Below 10% PVP the mats morphology is non-uniform, consisting of beads and fibers. Above 10% PVP, only flat and uniform fibers were observed. This paper outlines the dominant mechanism governing the mats shrinkage during heating. In addition, the effect of PVP concentration on the expansion of fibers diameter was investigated and found to be consistent with the linear shrinkage observing a minimum at approximate to 10% PVP. The effect of applied voltage on mat shrinkage was investigated, and showed a minimum at 12 kV. Understanding the interplay between fibers morphology and thermal shrinkage allows precursor composition and system optimization needed for minimizing shrinkage negative effects on the structure and properties of electrospun fiber mats. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 248-254