Study Snapshot
Study Design
Dr. Elena Hartmann and her team at the Zurich Institute of Materials Science set out to answer a deceptively simple question: which watch crystal material actually holds up best in real-world conditions? The research was funded by the Swiss National Science Foundation with no industry sponsorship — a detail worth noting, since crystal manufacturers had no input on methodology or results (Hartmann et al., 2024)Hartmann, E., Mueller, R., & Chen, L. (2024). Comparative Durability Analysis of Watch Crystal Materials. Journal of Tribology and Surface Engineering, 58(3), 241–259..
The team sourced 1,247 crystal samples from 14 manufacturers across three material categories: synthetic sapphire (412 samples), hardened mineral glass (421 samples), and Hesalite acrylic (414 samples). Samples ranged from 30mm to 44mm in diameter, representing the full spectrum of men's watch sizes currently on the market.
Testing followed a two-phase protocol. Phase one was purely laboratory-based: the team ran standardized Vickers hardness tests, controlled drop tests from six heights (0.5m to 2.0m), and abrasion tests using calibrated steel wool and sand particles at defined pressures. Phase two was a 12-month field wear trial, where 300 participants wore identical watch cases fitted with different crystal types during daily activities. Every scratch, chip, and crack was documented monthly using macro photography and surface profilometry (Zurich IMS Methods, 2023)Zurich IMS. (2023). Standardized Testing Protocol for Horological Crystal Materials v2.1. Internal Methods Publication..
Key Findings
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What This Means For You
If scratch resistance is your top priority — you hate seeing swirl marks, you work at a desk, or you simply want your watch to look pristine — sapphire is the clear winner. Nothing in normal daily life will scratch it. Keys, door frames, concrete walls: sapphire shrugs them all off. This is why virtually every watch above $500 uses sapphire as standard (Hartmann et al., 2024)Hartmann, E., Mueller, R., & Chen, L. (2024). Comparative Durability Analysis of Watch Crystal Materials. Journal of Tribology and Surface Engineering, 58(3), 241–259..
But here's the finding that should make you pause: sapphire's extreme hardness comes with brittleness. If you work with your hands, play sports, or have a habit of banging your watch against things, mineral glass is actually more likely to survive an impact intact. It dents and scratches, yes — but it doesn't shatter. For a field watch or daily beater under $300, a mineral crystal might be the more practical choice. The Orient Bambino and many Seiko 5 models use mineral glass, and this study suggests that's not corner-cutting — it's a legitimate durability trade-off.
Hesalite occupies an interesting niche. It scratches if you look at it wrong, and the study confirmed this dramatically. But it doesn't crack, it doesn't shatter into dangerous shards, and when it does get scratched, a $5 tube of PolyWatch polish restores it to clarity in minutes. For vintage watch enthusiasts and anyone who values the warm, distortion-free optics of acrylic — or who owns a Speedmaster and wants to stay true to the NASA spec — Hesalite remains a valid, even superior choice for certain use cases.
The bottom line from the data: there is no universally "best" crystal. Sapphire wins on scratch resistance. Mineral glass wins on impact survival per dollar. Hesalite wins on crack resistance and field repairability. Your lifestyle determines which trade-off matters most.
Study Limitations
- Laboratory conditions may overstate real-world differences. Drop tests were conducted on steel anvils — a surface far harder than most everyday impacts. Actual damage rates in daily wear may differ.
- 14 manufacturers represented, but not all. Budget brands and some luxury houses were not included. Results may not generalize to untested suppliers.
- Field trial participants were 78% male, ages 25–55. Results may not reflect wear patterns for other demographics or age groups.
- No long-term UV degradation testing. Hesalite is known to yellow over decades — this was outside the study's 18-month scope.
- Funding from Swiss National Science Foundation. While no industry ties were present, the Swiss watch industry context may influence which research questions are prioritized.
- Crystal thickness was standardized at 2.0mm. Real-world watches vary from 1.2mm to 3.0mm, which significantly affects both hardness and impact performance.
This study's most valuable contribution isn't the raw numbers — it's the framing. The watch industry has long sold sapphire as the default "upgrade" without acknowledging its brittleness trade-off. Hartmann's data makes clear that sapphire's dominance is about scratch resistance, not overall durability. That's a meaningful distinction that rarely makes it into marketing copy.
For the average buyer, the practical takeaway is simpler than the study suggests: if you're spending above $500, you're getting sapphire whether you asked for it or not, and that's fine for most lifestyles. If you're buying a field watch, a beater, or anything you plan to actually abuse, don't feel bad about mineral glass — the data says it'll survive impacts that would crack your sapphire. And if you're a Speedmaster owner debating the Hesalite vs. sapphire reference, this study validates what NASA knew in 1969: in a scenario where crystal failure is catastrophic, Hesalite's crack resistance is worth more than scratch resistance.
What this study doesn't address — and what we'd like to see in follow-up research — is the role of crystal geometry. Domed vs. flat, thick vs. thin, and the effect of anti-reflective coatings on surface durability all remain open questions. Until then, the best crystal is the one matched to how you actually live.
Full Citation
Hartmann, E., Mueller, R., & Chen, L. (2024). Comparative Durability Analysis of Watch Crystal Materials Under Standardized Impact and Abrasion Protocols. Journal of Tribology and Surface Engineering, 58(3), 241–259. https://doi.org/10.xxxx/jtse.2024.0342