An airbag can include a first cushion portion that defines a first inflatable chamber and a second cushion portion that is connected to the first cushion portion and defines a second inflatable chamber. The first inflatable chamber can receive inflation gas from an inflator to expand the first cushion portion, and the second cushion portion can receive inflation gas from the first inflatable chamber to expand the second cushion portion. A one-directional valve permits inflation gas to flow from the first inflatable chamber to the second inflatable chamber and restricts backflow of inflation gas from the second inflatable chamber to the first inflatable chamber.