Layer-multiplying coextrusion was used in conjunction with isothermal recrystallization to study the confined crystallization of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-tetrafluoroethylene (PVDF-TFE) using polycarbonate (PC) and polysulfone (PSF) as confining materials. Three layered systems were produced (PC/PVDF, PSF/PVDF, and PC/PVDF-TFE) with layer thicknesses ranging from 525 to 28 nm. The crystal morphology was affected by both layer thickness and recrystallization temperature. Specifically, increased recrystallization temperature and decreased layer thickness facilitated the formation of high aspect ratio in-plane crystals in both PVDF based polymers. On the other side of the spectrum, thicker layers and lower recrystallization temperatures produced on-edge PVDF crystals and isotropic PVDF-TFE crystals. The morphology was correlated with oxygen permeability, which decreased by almost two orders of magnitude compared with the bulk. A variety of crystal structures were obtained and explained with nucleation and diffusion theory. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1750-1761, 2011