Need to keep warm that hot dish that you're bringing to a potluck? Glass or ceramic are your containers of choice, as they are poor heat conductors, and the heat loss rate through the sides of the container will be much slower than if you use a metal container. Another thing to bear in mind is that as heat retention is affected by a dish's fat and moisture contents, something wet and fatty would be the way to go (after all, it is a potluck).
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