A continuously buildable mascara that stacks on infinite layers of volume and length with a bigger brush that delivers instant volume.Stack on infinite layers of volume and length MACStack Mascara. This never-before-seen, endlessly buildable, clump-resistant formula gives you customizable volume from natural to next-level, along with instant length. It features a Superstack Mega Brush, which is ideal for longer or upper lashes. Magnify your eyes and enlarge your lashes with this major mascara must-have.