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You can create your design by drawing it freehand, using a stencil, or even using a die-cutting machine if you have one.  Outdoor vinyl is waterproof, making it the best choice for use on drinkware. You can purchase outdoor vinyl at a craft or home supply store. Die-cutting machines often have pre-programmed designs for you to choose from, but you may be able to create an original design by experimenting with the software. Try tracing out letters to create a monogram, or use different colors of vinyl to create colorful hearts or polka dots. Once you have the design how you want it, carefully cut along the edges. Use caution when cutting with scissors or a craft knife, and never allow small children to handle sharp objects. Transfer tape is made to help you apply decals evenly. Lay your vinyl decal so that it’s facing up, then carefully apply a strip of transfer tape over the top of the entire decal.  If your decal has more than one piece, arrange the pieces exactly how you want them, then apply the transfer tape. This will help ensure they are spaced properly when you apply the decal to the tumbler. You can purchase transfer tape at almost any craft store. Once you’ve removed the backing, pick up the piece of transfer tape and lay it on the tumbler with the sticky side of the vinyl facing down.  It may help to have the tumbler laying on its side so you can see exactly where you’re applying the decal. Press firmly on the vinyl to ensure it’s fully adhered to the tumbler. If the vinyl decal doesn't lay flat, it won't stick properly to the tumbler. If you notice any bubbles or wrinkles, you can smooth them out with your fingers or with the end of a credit card. Once you remove the transfer tape, your design is finished! The outdoor vinyl should be long-lasting, although you may want to wash your tumbler by hand to help preserve your decal.
Trace your design on a sheet of outdoor vinyl. Cut out your applique using sharp scissors or a craft knife. Lay transfer tape over the top of your graphic. Peel the backing off of the vinyl and press it onto the tumbler. Smooth out any wrinkles or bubbles in the vinyl. Remove the transfer tape and enjoy your new tumbler!