translation.en: Shape-retaining is common in metal: you bend a piece of aluminum foil, and it holds its place. Contrast that with a plastic garbage can -- and you can push in the sides and it always bounces back.
translation.zh: 保持形状是金属的常性。你折起一片铝箔 ， 它就保持那个状态。相反的是， 一个塑料罐，你挤瘪， 它又弹回来恢复原状。