It's a Hollywood lie that is about to be exposed. Tape on the mouth will not keep a victim quiet. Unless they really want to be quiet and the script tells them to be quiet. Duct Tape is amazing invention. We have seen duct tape do many things on this very website. Despite the fact that you can build a canoe out of it or even remove hair with it, Duct tape will not keep a kidnapping victim silent.

The natural oils and moisture of the human skin work against the adhesive properties of duct tape. While the tape might keep a victim quiet for a few minutes eventually the adhesive will give way allowing the victim to create sound from their mouths. The victim can also introduce saliva on to the back of the tape from the mouth. This will speed up the deterioration of the adhesive as well.

I hope that you will never use duct tape to keep someone quiet, however if it is used on you, feel confident that you can escape eventually.