Cartesian Diver toy

A Cartesian diver is a classic educational toy and science experiment that demonstrates the principles of buoyancy and the ideal gas law. Typically consisting of a small, flexible container (often shaped like a diver, squid, or octopus) placed inside a water-filled bottle or glass, the 'diver' contains a small amount of air. When pressure is applied to the system, the air compresses, increasing the diver's density and causing it to sink.

While this specific glass and octopus-styled design is often handcrafted by glassblowers in regions like Germany or Italy, mass-produced plastic and glass versions are manufactured globally, particularly in China and the United States. These items are frequently sold by educational supply companies and boutique glass distributors rather than a single multinational corporation. Because it is a centuries-old scientific demonstration (named after René Descartes), it belongs largely to the public domain, with various independent manufacturers producing their own versions for classrooms and home laboratories.