How Do Insulated Thermoses Actually Work?

Whether you reach for your thermos to get a refreshing sip of cool water or extra warmth in the form of hot cocoa after a wintery hike outdoors, there's no denying we rely on our drinkware to keep beverages at the right temperature. Still, do you ever wonder how your insulated mug, thermos, or metal water bottle keeps your beverage either perfectly chilled or steaming hot? To better understand the science behind insulated thermoses, we asked YETI's senior engineering manager Bill Drinkwater to explain it all.

Tightly Sealed Inner and Exterior Vessels

Most thermoses rely on double- or even triple-wall construction, and the space between each wall is vacuum-sealed. Drinkwater explains that the first secret to the brand's success is the drinkware's secure inner and outer make-up. "Our cups are made from an inner vessel and an outer vessel," he says, "and there is a gap between those walls." Because it's devoid of air, this gap slows the transfer of heat—the less air, the less heat flow.

Welding Technology

To combat conductive heat transfer, the engineers at YETI only weld the two walls alongside the top lip of the product. Secondly, they minimize the effects of conductive heat transfers by removing a substantial amount of air between the walls. "Since convection works by transferring heat through the air, the less air we have, the less heat can be transferred through it," explains Drinkwater.

Radiant Barrier

You already know your YETI Rambler ($29.99, yeti.com) is tough, but for good reason. The final way the brand enriches the thermal retention is by adding a radiant barrier. This is done by applying a copper coating to the outside of the inner vessel to reflect radiation away from the contents of the cup.

Caring for Your Thermos

Purchasing an insulated thermos or water bottle is often an investment. To properly care for your thermos and prolong even something that's dishwasher-safe, Drinkwater advises that YETI products, for example, can be hand-washed with dish soap and warm water.