The first design is a flat rectangle folded from the full-sized 9 kbp scaffold (Fig. ). Its assembly requires 110 TFO staples, which stabilize 15 scaffold folds using the routing depicted in Fig 1g . The scaffold repeats seven 60R21N sections before looping back onto itself. The yield of well-formed rectangles was high (75%, n = 139) and showcases a characteristic elevation patterning caused by the wider tsDNA in the 60R21N pattern. The most common defect is "splitting" in which the staples failed to secure a scaffold fold. The observed length of the rectangle is 185 ± 7 nm, which fits reports that the rise between stacked bases in parallel DNA triplexes is the same as in B-DNA duplexes. The observed width is approximately 66 ± 4 nm, thus suggesting an effective helical diameter of 4.1 nm. This is a significant increase from the effective diameter reported for single-layer conventional DNA origami sheets (2.7 nm) and may be explained by the larger diameter of tsDNA, comparatively low crossover density in triplex origami, and the linker base in TFO staple crossovers. Notably, the triplex origami rectangle has almost twice the surface area of a single-layer DNA origami rectangle folded with the standard M13mp18 scaffold (Fig. , bottom) while using only half the number of unique starting materials (110 vs 220 staples).