In the 1890's, the Scottish chemist James Dewar prepared liquid oxygen in quantity and stored it in a Dewar flask. This is a double-walled flask with a vacuum between the walls. The vacuum will not transmit heat by conduction or convection, since both phenomena require the presence of matter. Heat is transmitted across a vacuum only by the comparatively slow process of radiation. By silvering the walls so that radiated heat would be reflected rather than absorbed, Dewar slowed down that process even further. (Our "thermos" of today is simply a Dewar flask with a stopper.)