A huff is an active breath out, used to move mucus towards the mouth where it can be easily cleared with a cough.
A huff is done with an o-shaped mouth and open throat. It is an active breath out, an active sigh, as if trying to fog up a mirror.
Once children are old enough, huffs should be part of all airway clearance routines and should be taught by the CF physiotherapist.
It can also be called a forced expiratory technique (FET)
When you huff you change the airflow in the airways by breathing out with more force than you breathe in. This helps to help move mucus towards the mouth.
It is important that huffs are not too hard as forcing air out can cause the airway to narrow or close. If you hear a wheezing sound, the huff may be too hard.
The huff creates squeeze points in the airway and moves the mucus towards the mouth so it can be coughed up, just like squeezing toothpaste from the tube.