The care for a thermos is easy. Try not to drop it or bang it around, which could break its seal on the vacuum. Keep smooth. The rest of the thermoses are not suitable for dishwashing. Often their lids are but the container may not be equipped to withstand a dishwasher's thermal cycle. When in doubt, hand wash. The temperature differential between the thermos and its surroundings to keep the contents hot or cold. For example, to keep coffee hot on a winter day, keep the thermos in a pack surrounded by something which will insulate it. Or keep it in your car, particularly if the sun is coming through its windows. Place the thermos in the shade or a cooler for keeping the contents cold. Be aware of where you are setting the thermos too. Setting it on ice would increase the rate of heat transfer, from the thermos to its surroundings. The coffee or cocoa will cool off quicker. A thermos with an insulated cap and a vacuum seal at its base prevents heat loss or benefits better than other designs, but regardless of design, the rate at which the thermos achieves temperature balance with its surroundings is somewhat common sense.