Thermo is a loan word that people hispanize as "termo" (the Spanish equivalent).
The noun "termo" in Spanish is formally recognized by the RAE to refer to a vacuum insulated food jar (such as the ones sold by Thermos®), and that is the word I was referring to, as it is the most widely identifiable use of the word "termo" in Spanish.
i.e.: "Pasame ese termo por favor?", "Se me ha quedado el termo en mi casa".