Recently, Sophie has created a number of projects that utilize double sided duct tape stickers. Here is her tutorial showing exactly how to make them. She uses them in her duct tape hat, animal face bags, and others.
template (if necessary)
Begin with a piece of parchment paper large enough for your image or template. Lay overlapping strips of duct tape on one side of the parchment paper.
Flip the parchment paper over and lay tape on the other side of the paper. Line this tape up with the tape on the other side.
Lay down your template and trace or draw whatever shape you would like your two sided sticker to be. This only needs to be done on one side.
Cut out your shape.
You now have identical stickers. Simply peel them off of each side of the parchment paper.
It's a slime-a-thon!