Rubber straps are not a single material: they're 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. I still hear people confuse them today, even those working in the industry.
FKM — the acronym for fluorocarbon elastomer family — is the material that has dominated demanding technical contexts in recent years. It resists hydrocarbons, dilute acids, salt water, and chlorine. Unlike silicone, it doesn't attract dust and doesn't deform from heat. It's stiffer 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 completely differently aesthetically.
The historical reference for this segment is the so-called Tropic, a term derived from the eponymous strap line produced by Zodiac in the 1960s for diving watches. The texture of regular reliefs — transverse ribs, sometimes a scale pattern — isn't decorative: it improves ventilation between strap and wrist in humid, warm environments, and reduces grip on a wetsuit. The original Tropic was vulcanized rubber; modern versions reinterpret that geometry in FKM or other synthetic elastomers. In the aftermarket and restoration world, the term Tropic-style now identifies any rubber strap with that characteristic ribbing, regardless of the exact material.
One texture variation 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 mimics the weave of a sail: you'll find it on the MoonSwatch, among others.
On the construction front, the most interesting case I know is Rolex's Oysterflex: a stamped metal exoskeleton embedded in elastomer. The result is a hybrid that behaves like a bracelet in terms of geometric rigidity, but has the flexibility and comfort of rubber. It's a sophisticated engineering approach, not merely a material variant.
A note on degradation: natural rubber ages through oxidation and ozone, hardens and cracks. FKM degrades much more slowly, but it's not eternal. Surviving vintage Tropic straps in good condition are rare precisely for this reason. When you see one intact after fifty years, you're looking at an exception, not the norm.