If you are not applying epoxy to seal it on to your tumbler, than yes, the outline will show. If you are applying epoxy over the Stickercal the clear outline of it may show depending on the style and color of the cup it is being placed on, but is typically blending in with the cup after a layer of epoxy is applied. At times, after epoxy, the clear outline may still faintly be visible, and again this will depend on the design/color of the cup. Typically on lighter color and glitter tumblers, the outline is rarely noticeable, but may show faintly on dark solid color tumblers. Stickercals can be applied to more than just tumblers - just keep in mind their clear outline will be visible.