What is the Mouthfill Equalisation
- sfsdiving
- 6 days ago
- 3 min read
The mouthfill is an advanced freediving equalization technique that transformed how divers go beyond their residual lung volume. It allows divers to reach impressive depths safely, reducing the risk of pulmonary edema and other lung injuries.
What is the Mouthfill?
At its core, mouthfill is a method of storing air in your oral cavity to use it for equalising. It’s essentially an evolution of the frenzel technique. Most divers learn frenzel by using the tongue: air is trapped behind it, then pushed upward to increase pressure, equalizing the ears. Mouthfill takes this a step further by letting you compress air not only with the tongue but also with the cheeks and jaw. In short, it’s frenzel amplified.
Why Learn Mouthfill?
Mouthfill protects your lungs at depth. As you descend, pressure compresses your lungs. Eventually, you reach residual volume—the minimal air left in the lungs after a full exhale. Beyond this point, normal equalization becomes extremely difficult. Mouthfill lets you “store” air in your mouth and use it to equalize while keeping your lungs safer.
To do this, you push air into the mouth, lock it with the glottis, and compress it with your cheeks, jaw, and tongue. Doing this near or past residual volume can be risky, so mastering control is essential.
When Should You Start Learning Mouthfill?
You can start whenever you’re curious, but some indicators suggest you’re ready:
You’re comfortably diving using frenzel to depths of 35–40 meters without strain.
You have strong control over the tongue and all three frenzel “locks.”
Constant vs. Sequential Pressure
Constant pressure: maintaining pressure continuously to keep the tubes open.
Sequential pressure: increasing and decreasing pressure in intervals, like a drumbeat.
Both methods work, but constant pressure demands more control. Choose the approach that feels natural to you.
At What Depth Should I Start Charging Mouthfill?
This depends on your target depth and how fully you can charge your mouth. Generally, divers begin around 15–20 meters. With good technique, mouthfill can support dives to much greater depths. Charging too close to critical lung volume, however, can be stressful.
Dry Practice is Key
Never expect to master mouthfill underwater first. Dry practice builds awareness and motor control without the stress of breath-holding. Use mirrors, balloons, or other tools to practice compressing air and controlling the oral cavity. Start with low-stress exercises and gradually add difficulty.
How Deep Can Mouthfill Take You?
You can estimate it using this formula:
Mouthfill depth = Surface mouthfill depth × Charge depth
For example, if a diver charges the mouth at the surface (1 bar) and manages it to 30 meters (4 bar), the mouthfill reaches 4 bar. Charging at 20 meters (3 bar) could extend the mouthfill much deeper, depending on lung volume.
Why You Might Swallow Your Mouthfill
This usually happens due to:
Stress (fear, new personal best, challenging conditions)
Excessive pressure
Abdominal tension
Using the Oral Cavity as an Air Pump
Air can be stored in three areas of the mouth: behind the tongue, in the cheeks, and in the jaw. Once filled, you can compress the air to equalize your middle ears.
Five Key Areas for Self-Assessment
Adam’s apple & under chin: indicate tongue position.
Jaw: often overlooked but essential.
Base of tongue: central to controlling air movement.
Cheeks: vital for shifting and compressing air.
Dry practice in front of a mirror accelerates learning and helps you spot mistakes.
How to Take a Mouthfill ‘M’ Charge
The ‘M’ charge connects the nasal cavity to the oral cavity. Pronouncing “MMMM” with lips closed opens the soft palate, letting air flow between cavities and creating pressure. Alternate ‘M’ and ‘B’ sounds to improve awareness of the soft palate and glottis.
Glottis Control
The glottis, the flap between the vocal folds, is crucial for both frenzel and mouthfill. Exercises that train awareness and control, like holding air in the mouth while shifting pressure, are essential.
Strengthening the Mouth as a Pump
Tools like balloons or small EQ devices can help. Practice keeping the glottis closed while moving air from the mouth to the balloon. Start small, gradually increase, and repeat consistently.
Tongue, Cheek, and Jaw Movements
Tongue: tip near front teeth, pump the back up and down to move air.
Cheeks: smile slightly to shift air; keep tongue down and jaw still.
Jaw: bite gently to compress air, keeping tongue down and cheeks still.
Tips: start with small movements, repeat often, and build consistency. Once mastered, you can efficiently manage the oral cavity and shift air from mouth to nasal cavity.
Conclusion
Master mouthfill on dry land first in a stress-free environment. Some divers naturally favour cheeks, others jaws—identify and strengthen weak points. With patience and consistent practice, mouthfill becomes intuitive, making deeper, safer dives possible.
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