Polymer phase behavior may be exploited for smart material design and development. Notably, certain crosslinked hydrogels exhibit a volume phase transition, which is characterized by an abrupt change from a collapsed, dehydrated state to a swollen, hydrated state and is dependent upon the temperature and composition of the gel. Here, we describe and characterize a system where the volume phase transition is controlled by the isothermal addition and removal of CO2. Specifically, we systematically assess the effects of hydrogel composition on its properties including transition temperature shifts (i.e., the change in transition temperature upon CO2 addition and removal), swelling kinetics, and swelling extent. Over the range of compositions tested, we measured shifts in the transition temperatures of up to 8.6 °C, enabling swelling in response to CO2 with up to a five-fold increase in mass. By triggering repeated swell-shrink cycles via the addition and removal of CO2, the reversibility of the transition temperature shift and swelling response was assessed, and the morphological changes occurring through this cycle were observed using SEM. The tunable and easily fabricated system described and characterized in this work may help guide the design of CO2-switchable hydrogels for applications ranging from drug delivery to microfluidics.