I need recommendations for a thermos to keep food hot?

Looking for personal experiences with a thermos to keep food hot for my daughter to take to school. She complains that the food is barely warm after being in the thermos for 5 hours and that’s how long we need to keep it hot.

Thermos should be a small one since it is just for lunch. We’re not filling it with hot liquids for drinking all day. Brands, links to products and # of hours the food actually keeps hot is appreciated.