The secret to the TERK™ – bellows. The shiny corrugations of the bellows not only have an industrial chic look, but the increased surface area helps to regulate the cool temperature of the beverage inside. Metal bellows have been used for decades in a variety of applications including automotive, aerospace and medical. In fact, the makers of the TERK™ have been making bellows for years, but have now harnessed the power of this industrial application for the greater good: ice cold beverages.