PEP stands for Positive Expiratory Pressure. Bubble PEP is a treatment to help individuals who have a build up of phlegm (secretions) in their lungs. Bubble PEP can be used by individuals who have difficulty clearing secretions. Children have to be at least 3 years old in order to understand the principles of Bubble PEP and therefore use it. During treatment, you will be encouraged to blow big bubbles through water.