You can certainly breathe normally if you tape your mouth shut at night. Sticking on Zippit's sleeping strip ensures that breathing through the mouth is no longer the easiest option and therefore encourages nasal breathing. However, with some effort, you can still breathe through your mouth through the small opening in the strip. The use of Zippit is not recommended if you suffer from sleep apnea or a stuffy nose. Always consult a health professional if you are unsure about using Zippit.