The bottle should be really leakproof and have an insulated cap. Leakproof means that you can turn it upside down and shake with no spill. Thermos-Nissan has good choices such as the one mentioned or Backpacker. If the cap is not insulated, most heat goes out through there. Contigo and Kleen Kanteen are second rate but people are free to suggest what they want. Be prepared that a 16oz thermos bottle may have a diameter slightly above the standard bike bottle so it is good to combine the thermos with a tolerant cage such as Profile Design Kage.