Thermoses with plastic flask

Plastic

— this material is characterized by low cost and relatively low thermal conductivity (which helps to retain heat). On the other hand, the plastic surface does not tolerate prolonged contact with hot liquids: it can release unpleasant odours or even harmful substances. Thus, plastic flasks are relatively rare — mainly in thermos mugs, which, by definition, are not designed for long-term storage of hot drinks, as well as in inexpensive food thermoses.