Continuing from the last post, let’s dive into another urban myth about waterproofing:
“No matter how good the water resistance, watch out for steam in wet saunas because vapor can still get in.“
Before debunking this myth, let’s go over a few key concepts.
Pressure Equilibrium
In our physical world, two forces from different environments will always try to reach equilibrium (though there are exceptions).
Take ink dissolving in water as an example of concentration equilibrium. From the ink’s perspective, it keeps diluting, while from the water’s perspective, it gradually becomes inkier until both sides reach a balanced state. Many measurable factors like concentration, temperature, and humidity naturally flow from higher to lower levels until equilibrium is achieved.
The same applies to pressure. When something is divided into an inside and outside environment, pressure will move from the higher to the lower side until balance is reached. The stronger the pressure, the more advanced technology and design are needed to resist it.
For example, when water is supplied to homes from a high-pressure water pipe via a water utility, the household pipes receive it at medium pressure. Once you open the tap, the pressure lowers further to ambient pressure so you can use the water. A typical household water pressure is around 4.5 Bar, which is the pressure applied when there are no open outlets.
When the tap is opened, water flows from the high-pressure pipe to the outside (1 Bar), and since there’s no obstruction, the actual pressure drops to about 1.5–2 Bar. (At 2 Bar, it would be difficult to wash dishes as water would splash everywhere. Pressure at 3-4.5 Bar is extremely powerful!) When you close the tap, the pressure builds back up to 4.5 Bar.
Waterproof vs. Moisture Resistance
Waterproofing and moisture resistance are slightly different concepts.
Moisture resistance involves reducing or managing the presence of water vapor (humidity) without necessarily creating an entirely impermeable barrier. It involves controlling condensation and preventing vapor from affecting the target object. A simple example is applying oil to wood to prevent vapor penetration, or laying a tarp under a tent to stop moisture from seeping through from the ground.
Waterproofing, on the other hand, refers to completely preventing an object or surface from becoming saturated with water, including during full submersion. Waterproofing is applied to areas directly exposed to water or significant moisture. An easy way to explain waterproofing is using a waterproof case on a phone, allowing it to be used underwater without water intrusion.
If you check Namu Wiki, it divides waterproofing into two types: full waterproofing and daily waterproofing. Full waterproofing means no water seeps in even when submerged (up to a certain depth), while daily waterproofing refers to protection against minor water exposure, such as splashes or brief contact with water.
Some claim that Gore-Tex® is the ultimate in waterproofing. Gore-Tex® fabric has over 9 billion pores per square inch, which are about 20,000 times smaller than water droplets but 700 times larger than water vapor molecules. This allows vapor (sweat) to escape while blocking liquid water. DWR (Durable Water Repellent) coating makes water bead up and roll off the surface, preventing the fabric from becoming saturated, thereby enhancing overall waterproof performance.
However, Gore-Tex® is designed for conditions without pressure. When washed in a washing machine, the centrifugal force acts like water pressure, making the fabric absorb water. In high-humidity environments, Gore-Tex®’s breathability is also reduced because vapor transfer depends on humidity differences. When external humidity is high, the difference becomes smaller, reducing the force that drives vapor out, making it harder for sweat vapor to escape effectively.
Gore-Tex® is a remarkable material, but its inability to provide full waterproofing is why it cannot be used to make diving drysuits. The type of waterproofing we talk about with watches is full waterproofing, while this level of protection is closer to daily waterproofing.
Water and vapor are different states (liquid and gas) of the same substance—H₂O. The amount of vapor the air can hold is limited, and beyond that, excess moisture condenses into water droplets. By the way, the visible steam from cooking rice is not vapor but very tiny water droplets (condensation). Vapor is invisible.
The three main differences between waterproofing and moisture resistance are:
- Purpose: Waterproofing prevents water intrusion, while moisture resistance manages vapor (humidity) levels.
- Application: Waterproofing is for areas exposed to water, while moisture resistance applies to areas vulnerable to vapor.
- Materials: Waterproofing often uses tougher materials designed to completely block water, while moisture resistance can involve lighter, breathable materials.
In short, waterproofing must prevent water from being forced in under pressure (like water pressure), so the requirements are more demanding than for moisture resistance. Waterproofing naturally includes moisture resistance because it deals with pressure, while moisture resistance happens at equal atmospheric pressure with no significant force involved. Hence, moisture resistance requires simpler technology and design.
In fact, moisture-resistant wall clocks or moisture-resistant lights used in bathrooms or saunas, where there is no difference in atmospheric pressure, are designed as follows:
Moisture-resistant clocks have the dial and glass bonded together for sealing, and an O-ring, rarely seen in regular household wall clocks, is installed at the battery compartment.
CASIO explains that even with moisture and dust resistance, they cannot guarantee waterproof performance.
Similarly, moisture-resistant lights use O-rings to block moisture. To improve performance slightly, a locking mechanism is sometimes used—much like how food storage containers work.
Products designed for moisture resistance may support a certain level of light waterproofing, but they do not offer full waterproofing. If you submerge these products in water, they will quickly flood.
Air, Vapor, and Water
The air we breathe consists of nitrogen, oxygen, argon, carbon dioxide, and more.
For certain diving conditions, helium is mixed with air (Tri-Mix) to reduce the nitrogen buildup in the body. After a dive, as the diver ascends to certain depths for decompression, the helium inside the watch expands, but it can’t escape, causing the watch crystal to pop out. This led to the invention of the helium escape valve. Since helium molecules are much smaller than nitrogen or argon, they can pass through even the strongest water seals and greases.
By comparing the sizes of molecules like air, helium, vapor, and water, you can see why water or vapor can’t get in but helium can. Some people argue that vapor has 1,200 times more volume and 100 times more permeability because it lacks hydrogen bonding. If that were true, we’d also have argon or vapor escape valves.
When we breathe out in a diving bell, the vapor doesn’t penetrate the seals, regardless of hydrogen bonds. The same goes for argon, which is much smaller.
Temperature
Watches have a manufacturer-specified temperature range in which they maintain their accuracy and performance. Watches left outside this range may lose accuracy. Usually, however, body heat protects the watch, as it is worn on the wrist.
In dry saunas (low humidity) or wet saunas (high humidity), watches typically function normally as long as they are worn on the wrist. No matter how high the humidity, without a significant pressure difference, vapor won’t penetrate the watch. In extreme temperatures, it’s likely that a person would leave the sauna before the watch fails due to heat.
If the watch is not worn (e.g., left in a pocket or above clothes), it could be more vulnerable to temperature, so caution is advised.
When water ingress occurs in a watch, opening the case usually reveals signs of flooding around the crown, case back, or near the waterproof seals. However, if those areas are clean and condensation is forming inside the glass, it’s likely that moisture entered during the assembly process and couldn’t escape. As a result, temperature or pressure differences could cause condensation, much like how condensation forms on a cold glass of water in summer as the water vapor in the air cools down.
Watches are more vulnerable in cold temperatures than in hot ones because the sealing and grease need to maintain tension and viscosity to preserve the airtightness. In cold temperatures, they harden and fail to function properly.
Citizen’s manual includes precautions regarding waterproof and moisture-resistant performance in hot springs, so I reached out to them for clarification:
Q. When the waterproof condition is perfect, can steam penetrate the watch?
A. Moisture already inside the watch can condense.
Q. So, when the waterproof condition is perfect, external steam cannot enter?
A. Yes, only internal moisture can condense, but no external moisture can enter.
Some people claim that switching between hot and cold water, like when washing dishes, causes the watch to draw in water, similar to how a fire cupping glass works by creating suction. However, the temperature difference alone cannot create enough pressure to breach the watch’s waterproof seals.
In fire cupping, the fire burns the oxygen inside the cup, converting it to carbon dioxide. As carbon dioxide molecules are fewer than oxygen molecules, the pressure inside the cup decreases slightly. The skin is then sucked into the cup as it tries to fill the vacuum. However, since there is no combustion inside a watch, there’s no meaningful change in internal pressure.
Sinn’s product description mentions a feature related to dehumidification (not moisture resistance), so I asked them for clarification as well:
Q. Your product description for the Ar dehumidification feature seems to defy the laws of physics—can you explain this in detail?
A. If the gasket ages, there could be problems, but under normal conditions, it’s impossible.
Q. So, under normal waterproof conditions, no steam can penetrate, correct?
A. Yes, you’re absolutely right.
Conclusion
If the watch’s waterproofing is in good condition and you’re using it within the temperature range specified by the manufacturer, there’s no need to worry about moisture or vapor. Just make sure to follow the inspection intervals recommended by the manufacturer, as waterproof performance can degrade over time.
Tip: Never use chemical cleaners when cleaning your watch. Harsh chemicals like alcohol, acids (detergents), or alkalis (bleach) can break down the greases and harden the seals, leading to reduced waterproofing. It’s best to use neutral soap or water.
As always, remember that your watch’s waterproof performance is exactly as good as you think it is. Follow the inspection schedules, read the manufacturer’s manual, and enjoy your watch responsibly!
Although I only covered one myth this time, I’ll wrap up the waterproofing topic and move on to a different subject in the next post.
