As dive watches became popular in the early 1960s, a need arose for a flexible, comfortable, and durable strap material. Most watches at the time shipped with metal bracelets, but these were ill-suited for dive use. So many divers opted for leather or canvas straps that quickly degraded in use, especially in salty ocean water.
The Tropic company developed a flexible rubber material and came to market in the 1960s with a distinctive strap for diving use. Although the earliest models were less supple, later vintage examples have stood up extremely well. Tropic developed this strap to be disposable and easily replaceable but many remain in use 50 years later.
The company mass-produced these straps, so new old stock still surfaces fairly regularly, giving vintage dive watch owners access to an authentic vintage accessory. Note that vintage Tropic molds are still in use by other companies, leading to some recently-produced straps being called “original” or “vintage”.
Note that the Tropic company's name can cause some confusion with the “tropical” faded dials on some vintage watches.
Tropic no longer exists as a company, but their name and design has become a standard term in the industry. Today, any thin rubber dive strap with a basket weave pattern is referred to as a “Tropic strap”.
The Tropic strap was a simple tapered affair with a blunt squared-off tongue. The outside had a basket weave pattern with ridges that resembled stitching along the edges. The same pattern is used on the loop in genuine Tropic straps, a feature usually missing on modern reproductions. The buckle is plain and squared off. On the back, a thicker crosshatch pattern was used with perforations that are barely visible on the other side. Some Tropic straps featured larger perforations and a different pattern inside. The tongue of the strap is plain on the inside surface. The later silicone rubber used by Tropic is extremely resistant to wear and liquids but does tend to attract dust.
Tropic also made other designs, including a popular driving strap with large holes. These are rarely associated with the company, however.