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Ladder graphs admit a maximum-symmetry embedding in which edges coincide. In folding ladders, there are no zero-length edges. We give examples of high-symmetry 3-periodic ladders, particularly emphasizing the structures of 3-periodic vertex- and edge-transitive folding ladders. For these, the coincident-edge configuration is one of maximum volume for fixed edge length and has the same coordinates as (is isomeghethic to) a higher-symmetry 3-periodic graph.

A brief introductory review is provided of the theory of tilings of 3-periodic nets and related periodic surfaces. Tilings have a transitivity [p q r s] indicating the vertex, edge, face and tile transitivity. Proper, natural and minimal-transitivity tilings of nets are described. Essential rings are used for finding the minimal-transitivity tiling for a given net. Tiling theory is used to find all edge- and face-transitive tilings (q = r = 1) and to find seven, one, one and 12 examples of tilings with transitivity [1 1 1 1], [1 1 1 2], [2 1 1 1] and [2 1 1 2], respectively. These are all minimal-transitivity tilings. This work identifies the 3-periodic surfaces defined by the nets of the tiling and its dual and indicates how 3-periodic nets arise from tilings of those surfaces.