The guest-free crystal forms of eight related small molecule cavitands (simplified nomenclature: R,R′,Y) are investigated as candidate discrete molecule microcavity materials (DMMMs). Due to their rigid bowl-like molecular structures, many cavitands are incapable of efficient crystal packing in pure form, yielding zero-dimensional porous apohost phases. By molecular modifications that eschew self-inclusion, emphasis is placed on engineering structures that exhibit uniform microcavities that are large enough to accommodate small molecules of interest (e.g., gases or volatile organic compounds). The most thermodynamically stable guest-free crystal forms of several cavitands—namely, H,H,CH2, H,Me,CH2, α-Me,H,CH2, Me,Me,CH2, Br,Me,CH2, Me,Et,CH2, Me,Et,SiMe2, and Me,i-Bu,CH2—appear to be as close packed as possible, yet they exhibit relatively large microcavities (or, zero-dimensional pores) in the range of 27–115 A3. Where self-inclusion is ineffective, the microcavities predictably assimilate the intrinsic ...