The Mouthfill Story

Did you know that the Mouthfill technique was invented in 2000? 

It was invented by Eric Fattah, who wrote the popular document on how to perform “The Frenzel Technique.”

Eric Fattah at Vertical Blue 2008

In freediving education today, beginners and intermediate freedivers are taught the Frenzel technique, which takes the freediver down to their Frenzel failure depth. At this depth, their lungs reach residual volume, typically around 30m. To go deeper still, advanced freedivers are taught the Mouthfill technique, which can take them to their breath-holding limits if performed correctly.

Before the Mouthfill technique was invented, the Frenzel was the only technique freedivers had to go deep. Advanced freedivers pushed their residual volume to their limits and trained their ability to continually pump air from their lungs into their mouth to Frenzel to depths past 60 and 70 m. But 80 m was where it became too hard to diaphragmatically transfer air from lungs to mouth. Hence, before 2000, few of the world’s best freedivers dove deeper than 80 m. 

It was not until a young competitive freediver, an engineering physics graduate from the University of British Columbia, conceptualized, practiced and perfected the Mouthfill technique, and tested it underwater at Alouette Lake in February 2000, that the freediving world received a gift that enabled the world’s best to go deeper than they had ever been before. 

Alouette Lake, British Columbia, Canada by by Lauren Kan on Unsplash

So what is this Mouthfill technique? 

Frenzel equalization requires a constant refilling of air from the lungs to the mouth to make air available for the tongue to push into the ears to equalize middle ear pressure. This is easy to perform at shallower depths, as there is still plenty of air in the lungs, but as one goes deeper, the air in the lungs is increasingly compressed. More and more effort is needed by the chest and abdominal muscles to contract and push that air into the pharyngeal space for equalization. Hence, all who use the Frenzel technique will eventually reach a depth limit, which is dependent on their lung capacity, whether they pack or not, and their intercostal and diaphragmatic flexibility.

The Mouthfill technique allows everyone who learns and practices it to surpass their Frenzel depth limit. 

During a chi gong meditation session in late December 1999, Eric Fattah pondered about a less effortful way for depth equalization when this idea came to him: What if you pushed a very large amount of air into your mouth just one time early in the dive and then trapped the air there?

Using his physics training, he pulled out his paper and pencil and ran the numbers on performing a Mouthfill at a shallow depth to see if this would offer an advantage. The math told him that it would offer a big advantage, and this early filling of air can be taken to a great depth.  

The genius of the Mouthfill is that it combines knowledge of Physics with Biology – Boyle’s Law with oropharyngeal anatomy and function – to solve one of the biggest limitations facing deep freedivers at that time.

The Mouthfill technique involves filling your mouth, cheeks, and throat at a depth, typically between 10 – 25 m – where you can still easily do so. And then holding your glottis shut, not to open it again until you reach your desired depth. During this time, you use your cheeks, tongue, and soft palate to manage the stored air by compressing and directing them through the Eustachian tubes and into the middle ear for equalization. This technique works because the percentage of pressure change decreases with increasing depth, so that one Mouthfill taken early in the dive, when it is still easy to draw air into the mouth, can last a long time. When performed correctly, a single maximum filling of the mouth and throat with compressed air and a tight noseclip at the surface can take one to a depth of 40 m.

Hence, Eric Fattah found an elegant solution to the limitation of the diaphragmatic Frenzel.

After his initial discovery, Eric Fattah took another year and a half to practice and perfect his own mastery of the technique. When he first began, he too had the tendency to swallow or “lose the mouthfill.” This advanced technique requires you to isolate the soft palate muscles from the vocal cords to use them independently. Being able to hold so much pressure in the cheeks and throat, while holding a lip seal, for a prolonged period of time also requires training of the orofacial muscles.

On August 11, 2001, he finally felt confident to use the Mouthfill technique at a world record attempt in his home waters at Ansell Point, in West Vancouver, British Colombia. And with his new innovation, he broke the world record with 82 m in 2’58”.

Photo of Eric Fattah by Peter Scott

This is the first world record set using the Mouthfill technique.

And this technique has revolutionized the freediving world. Take a look at our deepest freedivers today – Alexey Molchanov, Alenka Artnik, William Trubridge, Alessia Zecchini… Name any freediver who has surpassed the 100 m depth, and more likely than not, they all did it with the Mouthfill.

This technique resolved the Frenzel equalization dilemma and allowed freedivers to push their breath-hold to their limits during a deep dive, unencumbered by equalization issues. 

I share this piece of history with you because I think Eric Fattah should be recognized and remembered for his many innovative gifts to the freediving world. He is a freediving pioneer and innovator in so many ways. Not only did he invent the Mouthfill technique, he also invented the fluid goggles in 1998, experimented with FRC (functional residual capacity) diving to reduce narcosis, and made freediving computers that incorporated his freediving decompression algorithm to help deep freedivers avoid decompression sickness. 

His greatest gift to us was the Mouthfill equalization technique that allowed us the hope of surpassing our depth limitations, and going as deep as our mastery of the Mouthfill (with depth adaptation and training) will take us.

What lessons can we learn from the Mouthfill story?

We have many lessons to learn from this story. One, our sports is young and still developing. Many of the equipment we use today, like the fluid goggles, neck weights, lanyards… were invented fairly recently. Hence, if you have ideas, don’t be afraid to run with them. This story reminds us that we come from a line of explorers, problem-solvers, and creative innovators. There are problems in the freediving world now still waiting for us to shine light upon and bring our mutual intelligence to bear.

And second, I wish that we will continue to carry the spirit of Eric Fattah with us in our own equalization explorations. Whenever we are stuck with a problem or at a particular depth, I wish we do not give up and think we are just not cut out for it. But instead, may we have patience with ourselves to stay with the issue, study it, find alternative ways about it, meditate on it, try some chi gong, and have faith that there are sparks of genius within each of us waiting to be unleashed and to bring us to our next challenge.

Whatever your equalization issue is today, only you have the solution to it. No one will have the exact same body as you, and no one can know your body as well as you do. You may get tips and advice from experts and friends, but your body is uniquely yours, and only you can crack the code. And this website is set up to guide you in that process. We know so little about our bodies. Many muscles in our mouths, faces, and necks can be sensed, strengthened, made more supple and flexible, and used with greater skill and efficiency. 

I have developed an equalization course to help you understand your unique anatomy, with tips and advice to use your orofacial musculature with greater confidence and control. This course has launched in April 2022 and is available at

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