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The ‘Mouth fill’ technique… A step by step guide to deep equalisation

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If there is an equalisation  technique in freediving which is more talked about, strived towards, or mis-understood then I dont know about it. For many people it proves to be a nightmare to learn… it doesn’t have to.

The mouth fill technique is actually quite simple when you break it down in to steps and if you learn through dry land exercises. Before you attempt the mouthfill you need to know the Frenzel with 100% accuracy and efficiency, check out my breakdown of the frenzel here.


What is the mouth fill technique?

The mouth fill is an equalisation method which you employ when you reach your residual volume, or at least when equalising starts to become a bit more difficult than you would like. It involves using the cheeks as an air reserve and moving the tongue, neck/head and jaw to move that air in to the air spaces in your sinuses and ear.


It basically allows you to go deeper than conventional equalisation. I have used a single mouthfill from 10m all the way to 30m as a test. It’s very effective. When started deeper, say 25m it will take you very deep!

How does it work? Why does it allow us to go deep?

The mouthfill technique works because it uses air which is held in a relatively incompressible space, the mouth and the throat. The pressure changes at depth will not compress this space as much as the lungs so we have more control over its movement and distribution.


The Mouthfill technique… step by step

  1. As you start to reach your residual volume, lets say that’s at 30m, you need to start thinking about filling your cheeks with air.
  2. NOTE – you need to start the technique before you hit residual volume, or it will be too late.
  3. Extend your chin forward (head back looking down the line).
  4. Hold your nose tight.
  5. Fill your cheeks as much as you can keeping your teeth apart (an open jaw).
  6. Close your epiglottis.
  7. Keep your soft palate in the neutral open position ( and it needs to stay open the whole time, we are looking for constant equalisation).
  8. Then…one phase at a time…
  9. As you get deeper start to bring your chin back to normal diving position. This will compress the space and will push the air in to the only space it can go, where you need it in the sinuses etc.
  10. The next movement is to slowly close the jaw… compressing more air.
  11. The next stage is to use the muscles in the tongue  and neck to compress the space further.
  12. The final stage is to compress the cheeks until you are left with no more usable air to compress.
  13. The Mouthfill is now complete and you will have equalised deeper than you ever have before. woo hoo!


Difficulties in achieving success…

  • Stopping the air escaping from your lips. To stop this practice on dry land and learn to form an airtight and vice like seal with your lips.
  • Not following the stages in order. This simply take practice and should be again practiced on dry land until it is committed to memory.
  • Not closing the epiglottis and allowing the air to escape your mouth only to get lost in the lungs, or even worse… stomach. Practice closing the epiglottis by breathing out with a wide open mouth, and then stopping the air without using your tongue. This is the epiglottis doing its job.
  • Closing the soft palate thereby stopping the air from moving between the mouth and the sinuses / ears.  This is difficult to learn so there is an exercise which can help…. See below

Soft palate control…

The soft palate is a barrier of flesh between the nose and mouth/throat which moves through 3 positions, thereby opening the nose to the throat or closing it.

We are looking to maintain the neutral position, in the middle.

Practice finding these positions by blowing through pursed lips then blowing through your nose, in one breath. You will feel the soft palate move up and down. If you really focus you can find the position where it is half way and a bit of air will leave through your nose and mouth at the same time. This is the magical neutral position.

Ramp this up a notch by blowing up a balloon, closing your epiglottis, holding it to your lips then letting it release the air in to your mouth. Now focus on putting the soft palate in to neutral and the air should escape through your nose without obstruction!


You may find it easier and in many ways safer to practice the mouthfill technique during shallower dives. You don’t need to be doing really deep dives to practice it. I have had a student practicing it between 5 and 10m by incorporating exhale dives (exhale or RV dives to be discussed in another post).

Now… Practice, practice, practice….

I hope this guide will help you achieve success. If you have any questions feel free to send me a message.

All these techniques can be covered in our courses. Go to www.freediveuk.com for more details.

Dive safe!


4 Responses

  1. Thanks, this is a good write up. I am still having issues with the mouthfill, so I am going to try FRC/RV dives to get it right. Having to go to failure depth on full lungs every time is too much work…

    1. Just be carefull with frc. Most people overdo it in order to feel the effects shallower. You should be feeling a bit of a squeeze no shallower than 10m, aiming to load at maybe 7-8? everyone is different though.

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