noun
A container that keeps drinks hot or cold using a vacuum-insulated double wall. The term is neutral and widely understood.
寒い日は魔法瓶に熱いお茶を入れて持っていく。
On cold days, I put hot tea in a thermos and take it with me.
魔法瓶のおかげで、スープが昼まで温かいままだった。
Thanks to the thermos, the soup stayed hot until lunchtime.