A three-dimensional geometry is received, and sliced into layers. A first anisotropic fill tool path for controlling a three dimensional printer to deposit a substantially anisotropic fill material is generated defining at least part of an interior of a first layer. A second anisotropic fill tool path for controlling a three dimensional printer to deposit the substantially anisotropic fill material defines at least part of an interior of a second layer. A generated isotropic fill material tool path defines at least part of a perimeter and at least part of an interior of a third layer intervening between the first and second layers.