The AP × Swatch Royal Pop ships with a silicone rubber strap. The aftermarket offers options in leather, NATO, and various rubbers. After 60 days of materials testing, we settled on FKM Viton. Here's why it's the right material for this watch — and what makes FKM different from the alternatives.
The materials shortlist
When designing the Royal Pop strap, we evaluated four material families: standard silicone rubber (the original Swatch material), FKM Viton fluoroelastomer (the high-end watch industry standard), full-grain leather (heritage strap material), and NATO/nylon webbing (casual sport option). Each was tested against six criteria: water resistance, UV resistance, abrasion resistance, color stability over time, comfort against skin, and visual coherence with the watch. FKM Viton won on five of the six criteria.
FKM Viton: the material specification
FKM is the chemical industry designation for fluoroelastomer — a family of synthetic rubbers developed by DuPont in the 1950s under the trade name Viton. Originally designed for aerospace and automotive applications (engine seals, fuel system gaskets), FKM made the jump to watch straps in the 1990s when premium brands sought a material that outperformed silicone.
The Royal Oak Offshore line by Audemars Piguet has used FKM rubber straps since the early 2000s. Other notable users include Patek Philippe (Aquanaut), Hublot (Big Bang series), and Richard Mille across their sport collections.
FKM vs Silicone: the side-by-side
| Property | Silicone | FKM Viton |
|---|---|---|
| UV resistance | Fair (fades with prolonged exposure) | Excellent |
| Tackiness with sweat | Increases over time | Minimal change |
| Daily-wear durability | 2-3 years | 5-8 years |
| Cost (per kg, raw) | $5-10 | $50-80 |
FKM costs 5-10× more than silicone per kilogram of raw material. That cost differential is why most entry-level strap brands stick with silicone — and why brands targeting the premium segment use FKM.
FKM vs Leather: a different question
Leather is a beautiful material for dress watches and many heritage pieces. For the Royal Pop, leather is the wrong call. Water exposure (Royal Pop is rated 30m, leather hates water), color stability (saturated Royal Pop hues are technically challenging in leather dyes), and aesthetic register (leather signals dress watch, Royal Pop signals contemporary casual-luxury) all argue against leather.
FKM grade: not all FKM is created equal
FKM is not a single material — it's a family of polymers with different grades. Grade A (the watchmaking standard, optimized for prolonged skin contact) is what we use. Grade B (higher fluorine content, more chemical resistance, but harder), GF/GFLT (specialized for extreme temperatures), and ETP (maximum chemical resistance) are alternatives but generally overkill for daily wear.
Our sourcing
The Atelier Léman FKM is sourced from an Italian supplier (Solvay/Daikin family of suppliers) that has been producing watch-grade fluoroelastomer for over 30 years. Same supplier as several high-end Swiss watch brands. Color compounding is done at the supplier level to ensure pigment stability — we don't surface-dye the rubber, we have specific color masterbatches blended into the polymer at production.
The cost calculus
An Atelier Léman FKM Viton strap costs CHF 99 (Lépine) or CHF 129 (Savonnette). A comparable silicone strap costs CHF 30-60. The difference: 5-8 years of daily wear with no degradation versus 2-3 years before the silicone becomes tacky and discolored.
Cost per year of use:
- Silicone strap: CHF 30 / 2.5 years = CHF 12 per year
- FKM Viton strap: CHF 99 / 6 years = CHF 16 per year
The FKM is approximately 33% more cost per year, but represents a meaningfully better wear experience, better color, and better long-term aesthetic.
The bottom line
FKM Viton is the right material for a Royal Pop strap. Not because it's the most expensive option, but because it's the only material that aligns with the watch's positioning (sport-casual), use case (daily wear including water), and aesthetic (saturated colors that need to stay saturated). Silicone is cheaper but degrades faster. Leather is a beautiful material but wrong for this specific watch.