A method for generating three-dimensional toolpath instructions for a three dimensional printer, the method comprising: receiving a three-dimensional geometry; slicing the three-dimensional geometry into layers; generating an isotropic fill material tool path; generating an anisotropic fill tool path; creating an instruction file for controlling the three dimensional printer based on the isotropic fill material tool path and the anisotropic fill material tool path, the instruction file configured to control the three dimensional printer to print a 3D part by: - depositing a substantially isotropic fill material along the isotropic fill material tool path, wherein the generated isotropic tool path defines at least part of a perimeter of the first layer; - depositing a substantially anisotropic fill material along the anisotropic fill tool path, wherein the generated anisotropic fill tool path defines at least part of an interior of the first layer; and - orienting an anisotropic characteristic of the substantially anisotropic fill material to follow a trajectory of the anisotropic fill tool path such that the first layer of the 3D printed part exhibits the anisotropic characteristic in a specific direction corresponding to the trajectory of the anisotropic fill toolpath, wherein the trajectory of the anisotropic fill toolpath includes a connected sequence of path commands including path coordinates which are calculated according to the received three-dimensional geometry to provide part strength in the specific direction and to increase the strength-to-weight ratio. receiving a three-dimensional geometry; slicing the three-dimensional geometry into layers; generating an isotropic fill material tool path; generating an anisotropic fill tool path; creating an instruction file for controlling the three dimensional printer based on the isotropic fill material tool path and the anisotropic fill material tool path, the instruction file configured to control the three dimensional printer to print a 3D part by: - depositing a substantially isotropic fill material along the isotropic fill material tool path, wherein the generated isotropic tool path defines at least part of a perimeter of the first layer; - depositing a substantially anisotropic fill material along the anisotropic fill tool path, wherein the generated anisotropic fill tool path defines at least part of an interior of the first layer; and - orienting an anisotropic characteristic of the substantially anisotropic fill material to follow a trajectory of the anisotropic fill tool path such that the first layer of the 3D printed part exhibits the anisotropic characteristic in a specific direction corresponding to the trajectory of the anisotropic fill toolpath, wherein the trajectory of the anisotropic fill toolpath includes a connected sequence of path commands including path coordinates which are calculated according to the received three-dimensional geometry to provide part strength in the specific direction and to increase the strength-to-weight ratio. - depositing a substantially isotropic fill material along the isotropic fill material tool path, wherein the generated isotropic tool path defines at least part of a perimeter of the first layer; - depositing a substantially anisotropic fill material along the anisotropic fill tool path, wherein the generated anisotropic fill tool path defines at least part of an interior of the first layer; and - orienting an anisotropic characteristic of the substantially anisotropic fill material to follow a trajectory of the anisotropic fill tool path such that the first layer of the 3D printed part exhibits the anisotropic characteristic in a specific direction corresponding to the trajectory of the anisotropic fill toolpath, wherein the trajectory of the anisotropic fill toolpath includes a connected sequence of path commands including path coordinates which are calculated according to the received three-dimensional geometry to provide part strength in the specific direction and to increase the strength-to-weight ratio.