Well I'm doing the same project right now and our group has started the base of it.So we got a glass jar and first wrapped it around with tin foil.After that wrap that layer with black duct tape because it will absorb the heat. After that get duct tape and put cotton balls on it and put the thermos. You can put tin foil in side but that is a option. You can also put styrofoam inside.I would also recommend to put dead air inside so the heat can't escape. That is what I'm doing and I will message you my mark when I'm done with the thermos. I hope I helped a lot of people and Thanks.
