Airbag assemblies and active vents for airbag assemblies are disclosed. An airbag assembly can include an airbag cushion that defines an inflatable chamber and an active vent that comprises an aperture and a patch configured to plug the aperture. A first control tether is coupled to the patch and coupled to the airbag cushion. The first control tether is drawn taut as the cushion expands during deployment to draw the patch toward the aperture from a first position that allows unobstructed venting through the aperture to a second position that obstructs venting through the aperture. The first control tether, or a second control tether, is configured to be drawn taut to close the active vent. Responsive to impact with the airbag cushion, a control tether is configured to slacken to open the active vent.