“Our stainless steel water bottles keep hot liquids hot and cold liquids cold” This is the very saying you can hear from water bottle suppliers and manufacturers, since the invention of the insulated bottles. But how? The answer is foam or vacuum packing skills. However, there is more to stainless steel water bottles than to meet the eye. One heavy-duty bottle is a bottle within a bottle. What’s the deal? There is foam or a vacuum between the two containers. Containers filled with foam keep cold liquids cold while vacuum-packed bottles maintain hot liquids hot.