We report on the formation of tetragonally perforated lamellae from a polybutadiene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) (BVT) triblock terpolymer, PB 22P2VP 29PtBMA 49 110, in the bulk state (the subscripts denote the volume fractions of the respective segment and the superscript the overall molecular weight in kg/mol). The perforations are formed by the protrusion of the block with the highest volume fraction, PtBMA, through both the central perforated PB lamella and the two adjacent perforated lamellae of P2VP. The morphological characterization is based on transmission electron microscopy (TEM) and three-dimensional reconstructions using transmission electron microtomography (TEMT) experiments. In addition, SAXS confirmed an overall lamellar pattern. The so generated structures can be used for the fabrication of well-defined porous sheets with tunable size, as demonstrated by cross-linking of the central perforated PB lamella, followed by sonication-assisted dissolution into micrometer-sized lamellar particles with tetragonally arranged pores in nonselective solvents like THF.