A foldable cup faces a materials challenge every time it is packed away

Foldable products have an obvious advantage: they take up less room when they're not being used. But there is another side to that convenience that I find worth discussing.

Because the cup is designed to collapse and unfold, its material has to tolerate repeated deformation rather than simply maintain one fixed shape.

This brings us to elastomer fatigue. When a flexible material is repeatedly bent or stretched, tiny defects can eventually develop into cracks.

With enough cycles, those cracks may grow and lead to material failure. The result depends on several factors, including the material formulation, the amount of deformation, the geometry of the folds and the surrounding conditions. A material being flexible doesn't automatically mean it will tolerate unlimited folding.