Advanced Freediving Equalization: Frenzel, Mouthfill, and Reverse Packing Explained

Equalization is the single biggest reason divers hit a ceiling on their depth. Breath-hold can be trained, cold tolerance can be trained, comfort in the water can be trained — but if you cannot equalize at 40 feet, you will never hunt at 60. And if you cannot equalize at 60, you will never get to 100. The good news: equalization is a technique problem, not a physiology problem, and it is fully learnable. This guide walks through the three main freediving equalization methods, when each applies, and how to train them safely on dry land before you ever push depth in the water.

Why Valsalva Fails at Depth

Valsalva is how most people learn to equalize on airplanes and in swimming pools. You pinch your nose, close your mouth, and push air from your diaphragm up into your ears. It works fine on land and in shallow water.

Underwater, Valsalva starts breaking down around 30 to 40 feet and fails completely somewhere between 50 and 80 feet for most divers. The reason is mechanical. Valsalva relies on diaphragm pressure to push air through a long, narrow plumbing path. At depth, your lungs compress, the pressure differential collapses, and the diaphragm no longer has enough range of motion to generate the force you need. You try to equalize and nothing happens. Then you feel the pressure build in your ears, you back off, and the dive is over.

Any diver serious about hunting below 30 feet needs to leave Valsalva behind.

Frenzel: The Foundational Freediving Technique

Frenzel is the equalization method every freediver needs to learn. Instead of using the diaphragm, Frenzel uses the tongue as a piston. You close the glottis (the valve at the back of your throat), trap a small pocket of air in the back of your mouth, and use your tongue to push that air up into the Eustachian tubes. The diaphragm stays relaxed. The only thing moving is the tongue.

Because Frenzel only needs a small amount of air from your mouth, it keeps working long after the lungs are compressed. Most properly trained divers can Frenzel reliably to 60 or 80 feet without any trouble.

Learning Frenzel on dry land: pinch your nose. Close your mouth. Try to make a soft "k" sound without any air coming out. That tightening at the back of your tongue, against a closed glottis, is the action. Now say "TTT-TTT-TTT" silently, feeling the tongue push forward and upward. That forward-and-up piston motion is exactly what you use underwater. If you feel a small click or pop in your ears while practicing, you are doing it right. Drill this on dry land for weeks before trying it on a dive.

Common mistakes: using the diaphragm instead of the tongue (feels like Valsalva, just with nose pinched — this is not Frenzel); failing to close the glottis so the air escapes down the throat; trying too hard, which tires your tongue out. The technique should be effortless once you have it.

Mouthfill: The Technique for Deep Diving

Somewhere around 60 to 80 feet, Frenzel starts running low on raw material. Your lungs are compressed enough that there is very little air left to pull into the mouth. This is where mouthfill takes over.

Mouthfill is exactly what it sounds like. At a specific depth during your descent — usually 40 to 60 feet, while you still have air to spare — you take one big "fill" of air from your lungs into the cheeks, tongue, and mouth cavity. Then you close the glottis. Hard. From that point onward, you no longer pull air from your lungs at all. You equalize exclusively from the reservoir in your mouth, using Frenzel's tongue-piston motion.

The trick is the glottis lock. The glottis has to stay completely closed all the way to depth — if any air escapes back to the lungs, your reserve is gone and you cannot equalize. Most divers need months of practice to hold a reliable glottis lock under the stress of a deep dive. The timing of the mouthfill also matters; too early and your mouth empties before you hit depth, too late and you cannot fill the cheeks at all.

Done correctly, a good mouthfill extends reliable equalization to 100 feet and beyond. For anyone pushing past 80 feet of hunting depth, mouthfill is not optional — it is the technique that makes deep diving possible.

Reverse Packing: Advanced and Not for Everyone

Reverse packing is a technique for divers pushing beyond 100 feet who are running out of mouthfill reserve late in the descent. It involves a controlled pull of air from deeper in the respiratory system into the mouth cavity — essentially refilling the mouthfill from whatever is left in the lungs. It requires complete control over the glottis, diaphragm, and mouth, and it can easily cause lung squeeze or barotrauma if done wrong.

Reverse packing is an instructor-led technique. Do not try it from a blog post. A certified freediving course that specifically covers advanced equalization is the only safe way to learn it. Competitive freedivers and bluewater spearfishers who dive below 100 feet routinely use some version of it — and they all learned from a qualified coach.

Ear Anatomy Refresher

The ears you are trying to equalize are essentially sealed air chambers behind the eardrum. Each ear has an Eustachian tube that runs from the middle ear down to the back of the throat. Under normal conditions these tubes are collapsed shut. Equalization is the act of opening them briefly and allowing air from your mouth or throat to push up into the middle ear, matching internal pressure to the water outside.

Congestion, allergies, a cold, and even poor sleep can swell the tissue lining the Eustachian tubes. If the tubes cannot open on command, no amount of technique will equalize your ears. Diving congested is how you blow an eardrum or cause reverse block on the ascent. If you are stuffy, do not force it. Reschedule the dive.

Barotrauma: The Risks

Failed equalization has real consequences. Middle ear squeeze can rupture an eardrum. Sinus squeeze can cause bleeding from the nose during or after a dive. Reverse block on the ascent happens when air trapped in the middle ear cannot vent back out — this can be just as damaging as a descent squeeze and often more painful. Lung squeeze is a separate and more serious injury associated with deep diving and forced equalization; it is a genuine emergency and can end a diving career.

The cardinal rule: if you feel pain in your ears, sinuses, or chest, stop the descent, back off slightly, and try to equalize. If it does not clear in five to ten seconds, abort the dive and come back up slowly. Pushing through pain is how you hurt yourself.

Dry-Land Training Drills

Most equalization problems are solved on dry land, not at depth. Spend 10 minutes a day on these drills for a few weeks and your in-water equalization will transform.

Frenzel drill: pinch nose, close mouth, try to make silent "kah-tah-tah" sounds. You should feel your tongue pushing forward and up, and hear little clicks in your ears as they equalize. If you feel your diaphragm contracting, you are doing Valsalva — relax it and try again.

Glottis control drill: inhale, then close the glottis like you are holding back a cough. Hold for 10 seconds. Feel how the closed glottis completely isolates your mouth from your lungs. This is the same lock you use during mouthfill.

Mouthfill drill: take a normal breath, pull a big puff of air up into your cheeks (like puffing cheeks for a kiss), lock the glottis, and hold. Now try to Frenzel-equalize from that mouthfill without letting any air back into your lungs. If your cheeks collapse as you equalize, you are correctly using only the mouthfill air. If you feel your lungs empty, your glottis is leaking.

When to Call a Dive

Any of these are hard no-gos: sharp pain anywhere in the head, blood from the nose, vertigo, a sudden sense that one ear has "popped" differently than the other, ringing that persists after surfacing, or difficulty equalizing on the surface before the dive even starts. If your ears are not cooperating, trust the signal. The fish will still be there tomorrow.

Take the Course

Everything above is a starting point. Proper equalization training — especially mouthfill and reverse packing — should be learned with a qualified instructor in person. A certified freediving course (AIDA, PADI Freediver, Molchanovs, FII, SSI Freediver) will assess your technique underwater, correct errors in real time, and give you drills tailored to how your body actually behaves. This is not a topic where YouTube substitutes for a coach. Every experienced deep diver has a story about an instructor who transformed their equalization in a single session. Invest the time and money.

Check dive conditions before every session. For free California-focused forecasts, visit conditions.spearfactor.com.

Never dive alone. Always use one-up-one-down buddy protocol. For more on freediving safety, visit freedivingsafety.com.

Photos: "Freediving in the Ocean" by jayhem, via Wikimedia Commons (CC BY 2.0). Ear anatomy illustration by John Cunningham Saunders (1806), Wellcome Collection, via Wikimedia Commons (Public Domain).