Thanks everybody. I expected that the advice would be to stay away from the aluminum cups which is why I left them at the store until I asked about it here.

Quote Originally Posted by Art
I would've thought that due to the thinness of the container walls that there would be little difference between plastic and metal in this situation. Have you measured the transfer rate between the two container types?
Not formally, but from observation my metal graduate definitely conducts the water bath temperature quicker than my Jobo bottles and graduates.

Quote Originally Posted by Melanie
I use a old igloo, that i put warm or hot water depending on B/W or color film
I think that is important to specify that you are referring to an Igloo brand cooler. I'd hate to see a careless post result in an epidemic of homelessness among Eskimos