Vacuum, Double

The inner workings. (Tim Tomkinson)
Photo: Tim Tomkinson

A technology dating back to 1892 that suspends one container inside another, leaving a small amount of air between the two to insulate the inner contents from external temperature changes. (Shorter: Your coffee stays hot.) A modern thermos can keep cocoa steaming for hours in the backcountry. More important, the emergence of double-vacuum steins have doomed the beer koozie to irrelevance.

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