I am trying to build a homemade thermos. It needs to be able to conserve the heat in 125ml of water for 15 minutes.
However, unlike a normal thermos, it also needs to be able to be heated. What homemade substances can I use that are not flammable, yet provide a relatively high degree of insulation?
Note that my thermos will be heated with a flame from a candle for 25 minutes.