Soda cans

This watch may look like a heavyweight, but it’s not. It’s made of aluminium; the bottom of a soda can, to be precise.

Aluminum is a lightweight material that is at the same time flexible and durable, properties which make it perfect for the production of cans that contain carbonated beverages. Such cans are commonly shaped in cylindrical form, a design that engineers have developed as it enables fast production, caters to the needs of consumers and also saves costs of transportation due to efficient packaging and stacking.See Bill Hammack, The Ingenious Design of the Aluminum Beverage Can

The curved shape of the bottom of the can ensures it can bear pressure. The Hong Kong-based designer brand The Alchemist reuses the bottom of the can as casing for the clockwork and installs the clock's hands inside the negative space of the arcuate form.