A snorkel is a breathing tube that lets you inhale air from above the water’s surface while your face stays submerged. It works by creating an open airway between your mouth and the atmosphere, so you can float facedown and watch the underwater world without lifting your head to breathe. The concept is simple, but the engineering behind comfortable, safe breathing through a tube involves some interesting physics.
The Three Core Components
Every snorkel has three basic parts: a mouthpiece, a tube, and a clip or attachment that connects it to your mask strap. Most modern snorkels also include a purge valve near the mouthpiece and some form of water protection at the top.
The mouthpiece is made of soft, flexible material (almost always silicone) that you bite gently to hold in place. It forms a seal around your lips so air flows through the tube rather than leaking out the sides. The tube itself is a rigid or semi-flexible cylinder, typically 12 to 16 inches long, that rises from your mouth up past the waterline. That length keeps the opening above the surface while you float in a natural, relaxed position.
When you inhale, air travels down the tube and into your lungs. When you exhale, the used air travels back up and out. It’s the same principle as breathing through a straw, just wider and purpose-built for comfort.
Why Snorkels Can’t Be Longer
A common question is why you can’t just use a really long snorkel to breathe at greater depths. Two problems make this impossible. The first is dead space: the air sitting inside the tube after you exhale is mostly carbon dioxide. When you inhale again, you re-breathe that stale air before fresh air reaches your lungs. A standard snorkel adds about 160 to 170 milliliters of dead space to each breath. Your body compensates by taking deeper breaths (increasing what physiologists call tidal volume) rather than breathing faster. A longer tube means more dead space, more carbon dioxide rebreathing, and eventually dizziness or unconsciousness.
The second problem is water pressure. Even a meter below the surface, the surrounding water squeezes your chest enough to make inhaling through a tube to the surface extremely difficult. Your breathing muscles simply aren’t strong enough to expand your lungs against that pressure. This is why snorkels longer than 16 inches are not recommended, and why scuba divers need pressurized air delivered at the same pressure as the water around them.
How Breathing Resistance Stays Low
You might expect that breathing through a narrow tube would feel labored, but a well-designed snorkel barely changes the effort required. A classic J-shaped snorkel with an inner diameter of about 20 millimeters adds only 3 to 16 percent more airflow resistance compared to breathing without one. In a study of 19 volunteers, the actual energy cost of breathing with a snorkel (about 13.6 watts) was statistically identical to breathing without one. The tube diameter is the key variable: too narrow and resistance climbs sharply, too wide and the dead space problem gets worse. The 12-to-16-inch length and roughly 20-millimeter bore represent the sweet spot that manufacturers have settled on.
Clearing Water From the Tube
Water inevitably gets into a snorkel, whether from a wave splashing over the top or from dipping below the surface. There are two ways to get it out.
The old-school method is the “blast clear.” You exhale sharply and forcefully, blowing the water up and out the top of the tube like a whale spouting. It works, but it takes a strong puff of air and can leave some water behind.
Most modern snorkels include a purge valve at the bottom of the tube, right near the mouthpiece. This is a simple one-way flap: water that collects inside the tube pools at the lowest point, and even a gentle exhale creates enough pressure to push it down through the valve and out into the water. Air pressure from inhaling keeps the valve sealed shut, so no water comes back in. Think of it as a drain at the bottom of a bathtub. Before purge valves existed, water could only exit the way it came in, back up the full length of the tube. The purge valve lets gravity do most of the work.
Dry Tops and Splash Guards
To reduce the amount of water entering in the first place, snorkels come in three styles: classic (open top), semi-dry, and dry.
- Classic snorkels have a completely open tube. They’re the simplest and most reliable, but waves and spray can pour right in.
- Semi-dry snorkels have a splash guard at the top, a shaped deflector that redirects surface spray away from the opening. Water can still enter if you submerge, but casual splashing stays out.
- Dry snorkels use a float valve mechanism at the top of the tube. When the snorkel goes underwater, a small buoyant ball or disc rises and seals the opening completely. When you surface, the float drops and the tube opens again. This keeps the tube almost entirely water-free, even if you duck under briefly.
Dry snorkels are the most convenient for casual snorkelers who don’t want to deal with clearing water constantly. Some experienced snorkelers and freedivers prefer classic or semi-dry designs because dry tops can feel slightly more restrictive when breathing hard, and the sealed tube can create a slight suction sensation if the valve doesn’t open instantly on surfacing.
Why Silicone Matters for the Mouthpiece
The mouthpiece sits in your mouth for extended periods, so the material matters more than you might think. Silicone has largely replaced PVC (vinyl) in quality snorkels for several reasons. It stretches 300 to 800 percent before tearing and snaps back to its original shape, which means it conforms to your bite and lip shape without creating pressure points. PVC stretches only 150 to 250 percent and tends to crack after repeated flexing.
Silicone is also far more biocompatible. Allergy rates to silicone mouthpieces run around 0.3 percent, compared to 5 to 7 percent for PVC, largely because PVC leaches plasticizers (chemical softeners) into saliva over time. In seal testing across different face shapes, silicone achieved a 95 percent success rate for a watertight fit versus 70 percent for PVC. If you’re shopping for a snorkel, a silicone mouthpiece is worth the small price premium.
Full-Face Snorkel Masks
Full-face masks cover your entire face and let you breathe through your nose and mouth normally, which feels more intuitive for beginners. They use separate internal channels for inhaled and exhaled air: fresh air enters through the top of the mask and flows past your eyes (which also prevents fogging), while exhaled air exits through channels along the sides or chin and passes out through the tube.
The trade-off is a significantly larger dead space. A conventional snorkel’s dead space is about 160 milliliters. The breathing compartment inside a full-face mask holds around 250 milliliters when everything is working properly, but if the internal seals or valves aren’t functioning well, that can balloon to as much as 1,470 milliliters. A study in Diving and Hyperbaric Medicine found that full-face snorkel masks caused more frequent drops in blood oxygen and increases in carbon dioxide compared to traditional snorkels. This is especially concerning for children and smaller adults, whose natural breath volume may not be large enough to flush the extra dead space with each breath cycle.
For gentle, relaxed snorkeling in calm water, a well-made full-face mask works fine for most adults. But for anything involving exertion, currents, or repeated submersion, a conventional snorkel paired with a separate mask remains the safer and more reliable choice.