This is the 12720th most frequent Portuguese word.
térmico
Relating to heat or temperature.
Here, 'térmica' [thermal] is used as an adjective to describe the type of the bottle designed to maintain temperature.
Eu comprei uma garrafa térmica para manter o café quente.
I bought a thermal bottle to keep my coffee hot.
In this case, 'térmica' is used as an adjective qualifying 'propriedade' [property], denoting its relation to heat transfer.
A propriedade térmica do material influencia na eficiência energética da casa.
The thermal property of the material influences the house's energy efficiency.
Here, 'térmico' is an adjective qualifying 'comportamento' [behavior], focusing on heat-related characteristics.