Jan

Thanks everyone for replies. I didn't thought that it will be easy. I am quite sure that it would involve some innovation and smart brains - that's why I put the question here What about some substance that would be inside the plate (without access to air) that will keep it hot from inside when it absorbs it from environment? Something like those things: https://www.amazon.com/HotHands-Hand-Warmer-Value-Pack/dp/B0749NTTZN EdEarl: What temperatures: average to high, so the food has pleasurable temperature How much mass must be kept hot: plate with 300-400g of food/soup What kind of mass: food - meat, vegetables, soup, etc. How quickly does it cool: keep warm at least 20-30 minutes It would be exposed to the environment

Thanks DrP for your answer. I'd like to create special dishes for my father's restaurant. Their plates become cold very fast so they have to heat them up a lot. Waiters can't even carry them with bare hands and customer's food is cold within 5 minutes. If the plate can be warm for up to 30 minutes it would improve customers satisfaction a lot.

Hello, is there any material or substance or combination of both that will keep warm for at least 30 minutes after absorbing it from external source? Must be able to use for public purpose, in reasonable costs, no toxic materials. Most materials I know from real life that are used can be heated, but the heat goes off pretty quickly. Thanks, Jan