Hardlex Vs Sapphire: The Hard Truth About Dial Windows

So today we will be discussing two different types of glass used in watch dial windows. Hardlex Vs sapphire crystal. Most people seem to assume that sapphire is superior. But if you read on, you will find out that this is not necessarily the case.

As I’m sure you know, different watch types and brands use different materials for their windows. It is common to find windows made of materials such as mineral crystal, glass, or even plastic. Each one has their pros and cons. Some are cheaper, making for a less expensive watch, some are more scratch resistant, while others are more shatter resistant.

Well in this comparison we will be looking at the properties of hardlex and sapphire. Each has their pros and cons. By looking at these factors, we should be able to come to a satisfactory conclusion. First, let’s find out what exactly these two materials are in the first place.

Hardlex Vs Sapphire: What Are They Exactly?

In this section, I will offer a brief explanation of these two types of watch glass windows.


Hardlex is a special type of mineral crystal glass developed by Seiko. Now when we say “mineral crystal”, we are not talking about something you would dig out of the ground!

The type of mineral crystal we are talking about is synthetic crystals. These “crystals” are basically made of glass. What makes this glass different from ordinary glass is that it has been tempered.

What this means is that it has been heated to a high temperature. By doing so, the glass is less prone to scratches and more shatter resistant. So then what separates hardlex from any other mineral crystal glass?

The difference between Seiko’s hardlex and ordinary mineral glass is its hardness. Hardness as defined by the Mohs scale is the mineral’s resistance to scratches. The Mohs scale rates the hardness of a mineral from 1 to 10.

Most ordinary mineral glass will have a hardness rating of about a 5 or 6, while Seiko’s hardlex has a rating of 8. Therein lies the difference between ordinary mineral glass, and hardlex!


Once again, when referring to Sapphire crystal in a watch, this is not the same kind of sapphire gemstone found in jewelry!

The sapphire crystal found in watch windows is a synthetic crystal made from aluminum oxides. The way that they are actually made is by heating the aluminum oxide to extremely high temperatures. This in turn crystalizes the aluminum oxide. The resulting crystal has the same hardness as naturally occurring sapphire found in nature.

Because this synthetic sapphire is so hard, it requires specialized equipment such as diamond coated saws to cut it. This is the reason why it is more expensive.

You will often find that Sapphire crystal is used in many high end and luxury watches. But does this make it “better”? Read on to find out!

Hardlex Vs Sapphire: Scratch Resistance

hardlex vs sapphire scratch

We talked a little bit earlier about the Mohs scale, and how it measures the scratch resistance of a mineral. So this one is pretty cut and dry.

As we had previously stated, hardlex has a rating of 8. Synthetic Sapphire has a rating of 9 on the Mohs Scale. That is the same rating found in naturally occurring sapphire. A rating of 9 on the Mohs scale, means a mineral is second hardest next to diamond! Diamond is the hardest mineral with a Mohs rating of 10!

Sapphire is more scratch resistant than Hardlex. So that should be the end of this comparison, right? Not quite! There is still another factor we have to look at which is impact resistance.

Hardlex Vs Sapphire: Impact Resistance

hardlex vs sapphire impact

The next thing we will look at is the impact resistance of hardlex vs sapphire. Now you may think that since sapphire has a greater hardness rating, and is thus more scratch resistant than hardlex, it should be more resistant to impact. Well the actual answer may surprise you!

It turns out that despite the fact that hardlex is more prone to scratches than sapphire, it is actually more resistant to impact. How is this possible? This is because hardlex tends to bend more with impact. In this way it has a little “give”, which increases the threshold before it cracks or shatters. Even then, it will more likely crack, before it will shatter.

Sapphire, on the other hand, while not easily scratched, will be more likely to crack or shatter from an impact, such as being dropped or banged up against something really hard. It is solid and doesn’t have any give, therefore its impact threshold is lower. It is more likely to shatter from impact than to sustain a mere crack.

Can They Be Polished?

Should you happen to scratch either a sapphire or hardlex crystal watch window, you may be wondering of you can polish out the scratch. Yes it is theoretically possible to remove scratches from hardlex, or sapphire.

However, the better option in both cases would be to simply replace the dial window. The cost, time, and energy of attempting to fix it yourself, or get it fixed, in most cases, wouldn’t be worth the effort.

So Which One Is Better?

Well, let’s take a look at what we have learned so far.


  • Mohs rating of 8
  • greater shatter resistance
  • will crack vs shatter upon hard impact


  • Mohs rating of 9
  • lower shatter resistance
  • will shatter vs crack upon hard impact

What I get out of this is that the type of watch window you will want will depend on how you intend to use it. Sapphire is better as an everyday watch, or as a dress watch, while hardlex, is better for activities such as diving. This explains why we see so many luxury watches using a sapphire crystal window. And once again, hardlex can withstand more pressure, which is why you see hardlex being used in Seiko’s diving watches.

Now for your viewing pleasure, watch this guy scratch and smash the hell out of some watch windows!

The Takeaway

Aside from smashing watch glass with hammers, I think what we can get out of all of this is that the answer is not always so simple. Sometimes, such as the case is here, when you examine all of the factors, you will find that one thing may not be just “better” period, but rather better for certain applications.

I hope you enjoyed this article and gained some valuable information! As always, you can check out some more of our Vs articles here.

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3 thoughts on “Hardlex Vs Sapphire: The Hard Truth About Dial Windows”

  1. Good article, I’ve never scratched any Seiko watches accidentally. However, a correction, both Mineral Glass and Hardlex scratch at a level 6 with deeper scratches at a level 7. Hardlex definitely does not survive level 8 on the mohs scale. Hardlex is more shatter proof than normal Mineral Glass, similar to Gorilla Glass on phones being more shatter proof than standard mobile phone glass. Gorilla Glass also scratches at a level 6. Synthetic Sapphire as used in watch glass actually scratches at a level 8 on the mohs scale. Only pure natural Sapphire scratches at a level 9. I work in this industry, so thought it better to clarify things so people don’t get the idea that their watch is more scratch resistant than it actually is.

  2. Kind of surprised that people would assume something that is harder would have better impact resistance.

    Perhaps there is confusion between impact resistance and strength. Similar materials that are harder also have higher strength than their softer counterparts.


  3. Thank you Brian for your comment. Old phones may be a good source for glass to create replacement crystals… readily available in throw away phones.


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