The heat of a stored hot beverage is mainly lost to the colder air around it through conduction, and a cold beverage will gradually gain heat from the environment in the same way. A thermal or a vacuum bottle retards the transfer of heat (in either direction) between food and its surroundings by placing a poor heat-conducting medium between the two.
The basic difference between the vacuum and thermal storage bottles is the chosen medium. With a vacuum bottle, the medium is a near-vacuum that is hermetically sealed between the unit's inner and outer glass liners. In the case of the thermal bottle, the medium is a solid material that is a poor conductor of heat, but not as poor as a near-vacuum. Consequently, the vacuum bottle more efficiently impedes heat transference - and this capability is most pronounced when storing a hot beverage.
A thermal storage bottle does have a convincing selling point: It is less breakable, a pragmatic consideration when the user is a lunch-toting child.
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