A CPR mask is a barrier device that creates a barrier between a rescuer and a patient, preventing the exchange of bodily fluids and reducing the risk of infection during CPR or rescue breathing. It has a one-way valve, a pliable face seal for comfort, and a strap to secure it to the patient. To use it, ensure the patient's airway is open, position the mask over their mouth and nose, and seal it by applying pressure with the thumbs while using a C-grip with the fingers. The rescuer then blows through the mask's valve to deliver breaths, observing for chest rise to confirm a good seal.