rubber strap

Rubber for watch straps is not just one material: it is a family. From natural vulcanized rubber to synthetic elastomers like silicone, all the way to FKM (fluoroelastomer), each compound has a different mechanical and chemical profile. Confusing them is a mistake I still hear today, even from people working in the industry.

FKM — the acronym for the fluorocarbon elastomer family — is the material that has taken over in demanding technical contexts in recent years. It resists hydrocarbons, dilute acids, salt water, and chlorine. Unlike silicone, it does not attract dust and does not deform with heat. It is more rigid than pure silicone but softer than many composites. Baltic uses it on the Hermétique Enduropale, Girard-Perregaux on the Laureato Absolute Aston Martin with a fabric effect: the same class of material, rendered with completely different aesthetics.

The historical reference for this segment is the so-called Tropic, a term derived from the namesake watch strap line produced by Zodiac in the 1960s for dive watches. The texture with regular reliefs — transverse ribs, sometimes a scale pattern — is not decorative: it improves ventilation between the watch strap and wrist in humid and hot environments, and reduces adhesion to the wetsuit. The original Tropic was vulcanized rubber; modern versions reinterpret that geometry in FKM or other synthetic elastomers. In the aftermarket and restoration segment, the term Tropic-style now identifies any rubber watch strap with that characteristic ribbing, regardless of the precise material.

A texture variant is the hobnail, with small nail-like reliefs arranged in a grid: more tactile and less technical, used mainly for aesthetic reasons. Another approach is sailcloth printed in rubber, which imitates sail weave: you find it, among others, on the MoonSwatch.

On the construction front, the most interesting case I know is Rolex's Oysterflex: a stamped metal exoskeleton embedded in the elastomer. The result is a hybrid that behaves like a bracelet in terms of geometric retention, but has the flexibility and comfort of rubber. It is a sophisticated engineering approach, not a simple material variant.

A note on degradation: natural rubber ages through oxidation and ozone, hardens and cracks. FKM decays much more slowly, but it is not eternal. Vintage Tropic watch straps that have survived in good condition are rare precisely for this reason. Anyone who sees them intact after fifty years is looking at an exception, not the norm.