I saw a thread about this, and it seemed like everybody said that copper would keep coldest the longest. this is my problem that i need help with, I'm working a sushi catering company. I need to keep the sushi, cold, and presentable. if you google cooling trays there is a block of stainless steel for $89 with little feet pads for sale, that you stick in the freezer than take out. I feel like there is a better option, like i could go get a chunk of metal from somewhere right? and if I can, what is the best metal + volume i should get for this application. i want to be able to put at least 120 pieces of sushi on one.