Is the Hollis M1 Good for Freediving? Specs and Verdict

The Hollis M1 is good for recreational freediving in the top 10-15m (33-49ft) and a compromise below that. It is a frameless dive mask with one ultra-clear glass lens and a 100% pure silicone skirt, and Hollis describes it as low volume. What Hollis does not do is publish a volume figure, mention freediving on the product page, or market the M1 for breath-hold diving. It is a scuba mask with freediving-friendly traits, not a freediving mask.

That distinction matters because internal volume is the one spec that changes how a mask performs on a breath-hold dive. Every 10m (33ft) of depth takes one more mask-full of air out of your lungs just to stop the mask squeezing your face. A purpose-built freediving mask like the Cressi Nano publishes its figure, 85 cm³ (2.9 fl oz), so you can do that math. With the M1 you are working from the word "low".

If you already own an M1, use it. It is a reasonable mask for a first course or a reef day, as long as it seals on your face and you can pinch your nose through the skirt. If you are buying a mask mainly for freediving, a dedicated freediving mask from the roundup costs less and is designed around a minimal air space. The sections below show the specs, the physics and the depth at which the difference starts to count.

Hollis publishes a short spec list for the M1, and it is mostly about the lens and the skirt. The product page lists five features: a frameless 100% pure silicone skirt, an ultra-clear lens, wide vision and low volume, a fit for most faces, and a clear skirt option. The description adds that the lens is low-iron glass, which lets more light through and cuts the green tint found in standard glass, improving color and visibility in low light.

Lens

One lens of ultra-clear, low-iron glass, per Hollis. Retailer spec sheets list it as a single tempered lens. There is no center bar or frame edge across your view.

Frame

None. The M1 is frameless: the silicone skirt holds the lens directly, with no rigid frame around it.

Skirt

100% pure silicone, in black or clear. Hollis sells both at the same price.

Internal volume

Described as "low volume". No figure is published by Hollis.

Fit

"Fits most faces", in Hollis's words. Only a test on your own face confirms it.

Weight, strap, buckles

Not specified on the Hollis product page. Retailer sheets describe quick-adjust buckles mounted directly on the skirt.

Freediving or spearfishing use

Not mentioned by Hollis. Marketplace listings that put "freediving spearfishing" in the M1's title are seller copy, not Hollis claims.

Where the M1 sits in the Hollis mask line

None of the four Hollis masks has a published volume figure. All are described as low volume. The M1 has been on sale for a long time: the customer reviews on Hollis's own product page go back to March 2015.

Hollis does not publish an internal volume for the M1, and retailer spec sheets list it only as "Low". If you see an exact milliliter figure quoted for the M1, ask where it came from, because it is not on the manufacturer's page. This is not unusual. Among the manufacturer pages checked for this article, only Cressi's gives a number.

The design tells you something. A frameless mask has no rigid ring holding the lens away from the skirt, so the glass can sit closer to your face than in a framed mask of similar size, and less air fills the gap. That is the basis for calling it low volume. Dedicated freediving masks take a different route: Cressi gets the Nano to 85 cm³ with two small, tilted lenses and a reduced lens-to-face distance. What the M1's design cannot tell you is how close it comes to that, which is the question that matters once you go deep.

How to estimate the volume yourself

1. 01 —Lay the mask lens-down on a level counter with the strap folded out of the way.
2. 02 —Fill a kitchen measuring jug marked in milliliters to a known level.
3. 03 —Pour water slowly into the mask until it reaches the edge of the skirt all the way around, including the nose pocket.
4. 04 —Read how much water left the jug. That is the space inside the skirt.
5. 05 —Repeat twice and average the three readings.
6. 06 —If you own a mask with a published figure, such as an 85 cm³ Cressi Nano, measure it the same way. If your method reads high on the Nano, it is likely to read high on the M1 too, so compare the two readings rather than trusting either as exact.

The result is an upper bound, not the air space on your face. Your forehead, cheeks and nose take up part of that volume once the mask is on, and a soft frameless skirt sits differently on each face. Still, it gives you a real number to put into the depth table further down, which is more than the spec sheet does. The site's guide to low-volume freediving masks covers the general case for volume beyond this one model.

Internal volume matters because the air in a mask shrinks with depth and has to be topped up from your lungs. Boyle's law says that at a constant temperature, the volume of a gas is inversely proportional to its pressure: double the pressure and the volume halves. At the surface you are at 1 atmosphere. Every 10m (33ft) of seawater adds roughly one more, so you reach 2 atmospheres absolute at 10m, 3 at 20m (66ft) and 4 at 30m (98ft).

A review of deep breath-hold physiology in Frontiers in Physiology states it directly for the lungs: gas volume halves at 10m (2 atmospheres absolute) and falls to one third of its starting volume at 20m. The same rule puts it at one quarter at 30m. The air trapped in a mask behaves the same way. If you add nothing, the mask presses into your face as you descend.

DAN describes the result, mask squeeze or facial barotrauma, as a failure to equalize the air space between the mask and your face. The tissues under the mask are pulled into a vacuum-like space and small blood vessels engorge. The fix is to breathe small amounts of air out through your nose into the mask as you go down. That air comes from the same lungs you are diving on, and on a breath-hold dive there is no tank to replace it.

The mask is also not the only space competing for that air. Your ears and sinuses need it too. The same Frontiers review notes that a larger lung volume gives a diver more air to equalize the ears and sinuses at depth. Air spent on the mask is air that is no longer available for the ears, which is why freedivers care about a number that scuba divers, breathing from a tank, can mostly ignore.

The air a mask takes is its volume multiplied by the extra atmospheres of pressure. To keep a mask of volume V at its full size at an absolute pressure P, you need V times (P minus 1) of surface air added to it. At 10m (33ft) that is one mask-full, at 20m (66ft) two, and at 30m (98ft) three. The table runs that math for two published figures and two example volumes that bracket where an unmeasured mask might fall.

The figures are surface-equivalent air: the amount the gas would take up back at the surface. The 85 ml figure is Cressi's published volume for the Nano, and the 110 ml figure is the volume Omer gives for its Aqua mask, as reported by Apnea Passion magazine. The 150 ml and 200 ml columns are not claims about any product. They show what happens if a mask turns out larger than a dedicated freediving mask.

Read across the 30m row. Between the 85 ml mask and the 200 ml example, the gap is 345 ml of surface air on one dive, close to the 355 ml in a 12 fl oz soda can. At 10m the same gap is only 115 ml. That is the whole argument in two numbers: the penalty for a bigger mask is small near the surface and triples by 30m. If you measure your own M1 with the method above, put your number in the formula and you have its real cost.

Next to masks built for freediving and spearfishing, the M1 uses the same basic materials, a glass lens and a silicone skirt, and falls behind on published data and price. The table below uses each manufacturer's own pages where they could be checked, plus Apnea Passion magazine's figures for the Omer models. Where a cell says not published, the manufacturer page checked in October 2026 did not give it.

Three things stand out. First, the Cressi Nano is the only mask here with a volume on its maker's product page, and Cressi markets it for advanced freediving and spearfishing. The Cressi Nano review covers its specs in detail. Second, the dedicated masks cost less: Cressi America lists the Nano at $89.95 and Mares lists the Sealhouette at $83.95, against $124.95 for the M1, as of October 2026. Prices change often.

Third, the M1 is the only single-lens mask in the group. That gives it an unbroken view with no bar between the eyes. Hollis lists no corrective lens option for it, while two-lens designs such as the Omer Alien take optical lenses. If you need corrective lenses for freediving, start with a two-lens mask. If you do not, the M1's lens is one of its real strengths.

The volume difference starts to matter somewhere around 15-20m (49-66ft) and becomes hard to ignore past 20m. There is no switch at one depth. The cost grows by one mask volume per 10m, so the question is when that extra air begins to compete with what your ears need, and that depends on your lung size, your equalization technique and how many dives you do in a session.

0-10m (0-33ft): reef dives and snorkeling

Each mask costs at most one mask-full of surface air. The difference between the M1 and an 85 ml freediving mask is small, and fit and comfort matter far more than volume.

10-20m (33-66ft): shore spearfishing and early depth training

The cost doubles. Still manageable in any well-fitting low-volume mask, but a freediving mask starts to earn its place if you dive here often or do many dives per session.

20-30m (66-98ft): depth training

Three mask-fulls by 30m, taken while your lungs are squeezed to a quarter of their surface volume. This is where a mask with a known, small volume pays off.

Past 30m (98ft)

Every mask-full comes out of a small reserve. At these depths divers often equalize from a mouthful of air taken earlier in the dive rather than straight from the lungs, so mask air is at a premium.

Repetition matters as much as depth. If you make 30 dives to 12m (39ft) in an afternoon of spearfishing, you pay the mask cost 30 times. Each dive is easy, but a smaller mask means slightly less work on every one. The trade-offs between hunting dives and training dives are covered in the guide to freediving and spearfishing.

The M1 suits divers who want one mask for scuba and shallow breath-hold diving, and it is a poor first choice for anyone buying mainly for freediving. The split comes down to depth, budget and whether you want a published volume figure.

Scuba divers who also breath-hold dive

If you already own an M1 for scuba and it seals well, keep using it for snorkeling and recreational freediving.

Shallow spearfishing and reef hunting

The single lens gives a wide, open view and the black skirt cuts glare. For hunting in the top 10-15m (33-49ft), the M1 is a reasonable tool.

Travel and backup

A frameless mask is low profile and easy to pack. As a spare on a dive trip, the M1 does both scuba and freediving jobs.

Freediving students heading past 20m (66ft)

Buy a freediving mask. The Cressi Nano and Mares Sealhouette both list for less than the M1, and both are designed around a minimal air space.

Divers who need prescription lenses

Choose a two-lens mask that accepts corrective lenses. Hollis lists no corrective lens option for the M1.

There is also a category the M1 is clearly better than: the high-volume snorkeling mask. If that is your other option, the comparison of a freediving mask versus a snorkel mask explains why a low-profile design like the M1 is the better tool even for shallow breath-hold dives.

Before you take the M1 freediving, check that it seals without the strap and that you can pinch your nose through the skirt. Hollis says the M1 fits most faces, but a soft frameless skirt either follows your face or it does not, and no spec sheet can tell you which. DAN describes the basic seal test: a mask should seal when you place it gently on your face and inhale through your nose, and stay on without the strap.

1. 01 —Move the strap out of the way, over the lens and off your face.
2. 02 —Hold the mask lightly against your face, with no pressure from your hand.
3. 03 —Inhale gently through your nose and let go. The mask should stay on by suction for several seconds.
4. 04 —If it falls or you hear air leak in at the cheeks, temples or under the nose, the skirt does not seal on your face. Try another mask.
5. 05 —With the mask on, reach up and pinch your nostrils through the nose pocket. You need a firm, easy pinch for the Frenzel and Valsalva maneuvers.
6. 06 —Look down as if descending head first. The skirt should not lift at the upper lip or press hard on the bridge of your nose.
7. 07 —Repeat the test wearing your hood, if you dive in one, because a hood can pull the skirt edge.

Strap tension does not fix a poor seal. A mask that only stays sealed when the strap is cranked tight is the wrong shape for your face, and on a freediving descent it also presses harder into your face, which is the opposite of what you want while you are adding air to it. Set the strap just tight enough to hold the mask in place during the duck dive.

Choose the black skirt for spearfishing and bright, sunny water, and the clear skirt for low light and photography. Hollis says the clear skirt version gives a brighter, more open view and improves peripheral awareness in low light. A black skirt does the opposite: it blocks light coming in from the sides, which keeps glare off the inside of the lens in bright water. Apnea Passion notes in its review of Omer's spearfishing masks that a matt black silicone surface also reflects less light toward fish.

Removing the factory film

A new M1 will fog until you remove the film left on the glass from manufacturing. PADI's guide to preparing a new mask explains that the lenses are coated with a thin layer of silicone at the factory and recommends scrubbing it off before the first dive.

1. 01 —Use a paste toothpaste, not a gel and not a whitening type. Whitening pastes contain crystals that can scratch the glass.
2. 02 —Put a small bead on the inside and the outside of the lens and scrub with a fingertip, working into the edges where the glass meets the skirt.
3. 03 —Never use a textured sponge or steel wool.
4. 04 —Rinse thoroughly in fresh water. If you are not in a hurry, you can leave the paste on overnight before rinsing.
5. 05 —Before every dive, rub a drop of defog or saliva on the inside of the lens and rinse it lightly.

For care, rinse the mask in fresh water after every session, dry it out of direct sun and store it where nothing presses on the lens.

You equalize the M1 the same way as any mask: small puffs of air through the nose, timed with each ear equalization. DAN's advice for preventing mask squeeze is to keep the nasal passages open on descent by blowing small amounts of air through your nose each time you equalize your ears. On a freedive, pairing the two keeps the mask topped up all the way down.

For the ears, many freedivers use the Frenzel maneuver: pinch the nostrils and contract the throat muscles to push air up, rather than the Valsalva's gentle exhale against pinched nostrils. To add air to the mask, you relax the pinch for a moment and let a little air out through the nose. Both moves depend on a nose pocket you can grip firmly through the skirt, which is why the pinch check belongs in every fit test. The Frenzel technique guide covers the tongue movement step by step.

Deeper dives change the budget. Once the lungs are compressed, divers take a mouthful of air partway down and use it to equalize the rest of the way. That reserve is small, and any air the mask takes from it is air the ears do not get. This is the depth range where a mask with a known small volume earns its price, and where the mouthfill technique becomes part of your training.

Whatever mask you dive, the rules that keep you safe do not change: dive with a trained buddy, add air early and often, and never force an equalization. Pain is a signal to stop and come up a little, not to push harder.