Hello, this is Classical.
In today’s post, we’re diving into another persistent myth in the world of watches.
Urban Watch Myth Series – Part 3:
“Even if a watch is waterproof, vapor can still get inside—so some brands fill them with special gases or oils.”
Let’s explore whether this claim holds up to science.
■ False Premise: “Waterproof ≠ Moisture-Proof”
Let’s get straight to the point: if a watch is truly waterproof, it is also moisture-proof.
However, the opposite is not true—moisture resistance alone does not guarantee water resistance, since waterproofing considers pressure integrity as a fundamental requirement.
Think about a Lock & Lock food container: even in a dry refrigerator, moist foods retain their water content because the seal keeps moisture in and external air out. That’s how easy it is to prevent vapor exchange when the seal is solid.
As mentioned in earlier posts, a watch that maintains its rated water resistance will not allow moisture in. Watches aren’t vacuum-sealed; they are already filled with air. And because no naturally occurring gas is smaller than helium, there is no scientific basis to say ambient vapor can seep into the case.
From a fluid dynamics perspective: if the inside is already full of air, no additional particles can enter without pressure exceeding the case’s rated specification.
■ What About Argon Gas?
Some brands claim they’ve enhanced resistance by filling watches with argon gas.
Argon exists naturally in the air. In diving, it’s used to inflate drysuits—especially in ice diving and technical diving. Why? Because it conserves breathing gas and retains body heat better due to low thermal conductivity.
That said, there’s no practical need to fill a watch with argon.
It might sound impressive for marketing, but functionally, there’s no real benefit over regular air. Most brands that used to make this claim have stopped doing so. Whether filled with air or argon, it makes no significant difference.
■ Oil-Filled Watches – Why Do They Exist?
Some watches, like those from Sinn or Resco Instruments, are filled with oil. But not to prevent vapor intrusion.
They serve two main purposes:
1. Increased Pressure Resistance and Simpler Design
Underwater, air volume changes most significantly with depth. Since a watch also contains an air-filled space, its case, crystal, and gaskets are specifically engineered to withstand water pressure. This design not only enables the watch to resist external pressure at depth but also to accommodate the internal pressure changes caused by the compression of the air inside the case.
As a result, compared to watches with lower water resistance, physically dive watches typically feature a thicker case and a more robust crystal.
With no air inside, there’s no need to account for gas compression. This allows brands to use thinner crystals and simplified internal structures—reducing both weight and production costs.
Just like oil-filled diving compasses can handle deep pressure despite their lightweight plastic housings.
2. Better Underwater Legibility
Underwater, objects appear about 30% larger due to light refraction between the mask and water. If air exists inside the watch case, it causes refraction between the crystal and dial, potentially leading to visual distortion.
Oil minimizes this effect, improving readability.
So, the purpose of oil isn’t waterproofing—it’s mechanical and optical optimization.
■ Scientific Perspective: Can Moisture Really Penetrate?
Watches are not vacuum chambers, but if their seals are intact, external air or moisture cannot enter.
In deep diving—usually below 65 meters—helium-based breathing mixes are used to reduce nitrogen absorption and improve decompression efficiency. These depths apply pressures over 7.5 BAR.
Even in such extreme cases, watches resist helium unless they are subjected to prolonged saturation and lack a helium escape valve.
Also, human exhalation contains about 6% water vapor(Moisture). In environments like diving bells or saturation chambers, everything contains moisture—air, food, and water alike.
But even then, vapor molecules are larger than helium, so they cannot naturally pass through a sealed watch.
■ In Summary:
- If a watch is waterproof, it is moisture-proof.
- Moisture cannot enter a sealed watch unless exposed to extreme pressure beyond specification.
- Special gases or oils are used for structural or visual purposes—not to block vapor.
Always approach watch claims with scientific understanding.
Don’t fall for fancy marketing—understanding physical properties and internal construction matters more.
Stay tuned for the next installment in our Urban Watch Myths series—where we’ll explore how temperature affects timepieces.
Thanks for reading!
