For reducing anthropogenic CO2 emissions, carbon capture and sequestration technologies benefit from the creation of new and efficient gas exchange systems. Vascularized systems provide a means of exchanging CO2 by providing high specific surface areas and patterned, intimate contact between capture fluids and gases. The well-defined geometrical arrangement of fluid and gas channels, separated by semipermeable membranes, also provides a new platform for augmenting the function of liquid chemical solutions to carbon capture. In particular, the separation distance of the channels, or polymer membrane thickness, is closely related to the absorption rate as gases must permeate through the membrane before reacting with a fluid. Here, a study of the relationship between the membrane thickness in 3D microvascular contactors and absorption rates via a selective etching process is reported. By decreasing the membrane thickness, the mass transport rate of CO2 in the vascular contactor is increased by up to 160%.