Tonneau

Tonneau takes its name from the French word for barrel. That is the shape: flatter top and bottom edges with sides that curve outward in between. It borrows the vertical proportion of a rectangle and the softened outline of a circle. That means it sits between the two in both looks and comfort. A cushion case is the near neighbor, a square with heavily rounded corners, and listings mix the two words freely.

Many tonneau cases curve along their length as well as their width, so the caseback follows the wrist instead of bridging across it. That makes the watch feel smaller than its dimensions suggest and stops it rocking on a curved arm. The same curve limits what fits inside: a domed caseback leaves less vertical room. That is why tonneau watches usually run slim movements rather than thick automatics carrying extra complications.

Costs follow the shape. Crystals, gaskets and casebacks are all custom, so replacement parts arrive slower and cost more than round equivalents. Straps are often integrated into the case rather than sitting on standard lugs. Stylistically it commits: a tonneau reads either strongly vintage or strongly modern luxury, with very little neutral ground in between.

Fit is worth testing in person, because the curve either matches your wrist or fights it. Rest the watch on your arm with the strap unfastened: a well judged tonneau touches along the whole caseback, while a mismatched one rocks on its center. Straps carry the running cost. Integrated bands are cut for one model, and they stop being made long before the movement wears out. Buy a spare with the watch if you plan to keep it.