From engineerguy.

Bill explains that the adhesive used in tape is a viscoelastic substance — a substance that can act like a liquid or a solid and that can be elastic. It is this behavior that allows duct tape to adhere with light pressure, hold tight, and let go when peeled from a surface. Bill’s ten-minute video about duct tape explains more: https://youtu.be/E-F2QQuZZGk.