I managed to get an extra day out of the batteries that seemed to have run out in the cold (see previous post). I kept the batteries in my pocket to keep them warm and was able to take this picture and another 30 besides! This flask interested me. Mine is a lovely shiny silver. Physics teachers are fond of pointing out that if hot objects are shiny silver, they are poor emitters of infra-red heat radiation whereas dull black surfaces are good emitters. I think an experiment is called for here to see if the black outer colouring does impair the performance. It is quite possible that so little thermal energy is expected to reach the outer wall in the time you'd want to drink that the outer colour is irrelevant.
