Can one put hot food into a Thermos on Shabbos?

Can one put hot food into a Thermos on Shabbos?

At the office where I work, there is no way for me to heat my lunch, becaucse I don’t use a microwave for health reasons. So, I bought a thermos, of the kind made for food, with an opening nearly as wide as the body. My colleague at ZoomTorah Meir, saw my hot...