I think it's an insulator
Tin is a good heat conductor. So to keep hot water in a tin can hot you need to insulate the outside and bottom of the can with something that does not absorb heat but instead contains it next to the can.
because it is a cold material
Not a requirement, but a very good idea if you plan on keeping it for a while.
Foil itself will not warm it, it has to already be warm for it to insulate it.
Both Good for keeping you warm; Bad for the environment
cotton is very good because it warms up your body others are too hard or not very helpful however, metal is good to because when you put tea or coffee in the metal cup it heats up and keeps you warm.
coldness is a way for hypothermia and keeping warm can prevent this. in Antarctica they wear very warm uniforms to prevent hypothermia.
Walking on snow, keeping warm in cold climates
it is a soup prepared in warm broth with peanut shellings put into a food processer and the put into the soup
soup,
very good indeed
Keeping warm is not a change - of any sort.