A level-4 Menger sponge 0.3mm wall-thickness. Only available in Frosted Ultra Detail.
Due to the small size of the holes, they get full of the wax of the support structure and must be removed with warm water or any product that disolves the wax without affecting the FUD material. Brushing can destroy the walls.
Check also the level-3 one: https://www.shapeways.com/model/245325/menger_frosted.html