Here are some regular patterns to be used as infill and internal structure for 3d models using OpenSCAD.

Version 1: Cone tubes
This structure consist of separate tubes with double cones. The tubes are arranged rectangular.

Version 2: Sphere tubes
This structure consist of separate tubes with spheres. The tubes are arranged hexagonal. The calculation is time intensive.

Version 3: Octahedrons
My favorite structure consist of linked octahedrons. The octahedrons are arranged rectangular. The wall size is at minimum.