The paper presents a method for creating size-selective membranes using porous graphene. The authors fabricate suspended graphene membranes over predefined wells on a silicon oxide substrate, which are then filled with gases to create microcavities. UV-induced oxidative etching is used to introduce pores in the graphene, allowing for the selective passage of smaller molecules while blocking larger ones. The transport of various gases (H₂, CO₂, Ar, N₂, CH₄, and SF₆) through the pores is measured using a pressurized blister test and mechanical resonance. The results show that the etched pores significantly increase the leak rates of H₂ and CO₂, while the transport of Ar and CH₄ remains unchanged. The molecular selectivity of the porous graphene membranes is demonstrated by measuring the time rate of change of membrane deflection, which is consistent with theoretical models based on effusion through angstrom-sized pores. The study provides experimental evidence for the use of graphene as a size-selective gas separation membrane, representing a significant step towards the realization of macroscopic, size-selective porous graphene membranes.The paper presents a method for creating size-selective membranes using porous graphene. The authors fabricate suspended graphene membranes over predefined wells on a silicon oxide substrate, which are then filled with gases to create microcavities. UV-induced oxidative etching is used to introduce pores in the graphene, allowing for the selective passage of smaller molecules while blocking larger ones. The transport of various gases (H₂, CO₂, Ar, N₂, CH₄, and SF₆) through the pores is measured using a pressurized blister test and mechanical resonance. The results show that the etched pores significantly increase the leak rates of H₂ and CO₂, while the transport of Ar and CH₄ remains unchanged. The molecular selectivity of the porous graphene membranes is demonstrated by measuring the time rate of change of membrane deflection, which is consistent with theoretical models based on effusion through angstrom-sized pores. The study provides experimental evidence for the use of graphene as a size-selective gas separation membrane, representing a significant step towards the realization of macroscopic, size-selective porous graphene membranes.