A flexible laminate for a package is described that includes an integrated one-way valve that allows gas generated within the package (e.g., carbon dioxide outgas) to be released to the external environment, while at the same time preventing environmental elements from entering the package. The valve is defined by the layers that form the flexible laminate, as opposed to being a separate structure that is attached to the flexible laminate. In particular, first and second cut lines are defined in a valve area of the first and second film layers of the flexible laminate structure in an offset manner. Oil is pattern-applied to one or both film layers in the valve area, and an opposing surface of one or both of the film layers further includes a surface treatment that decreases the amount of surface energy between the film layers to allow the valve to open at the desired pressure.