Which would (wood, glass, iron, steel) be the best material to use to separate heat from cold?

The best answer to this is Wood. It should be noted that wood does not burn from heat very easily. It may burn when it is exposed to fire but when separating heat from the cold, it will be very effective. It is not recommended to use steel because this can get hot very quickly. It can cause the person to get burned.

It is also not recommended to use glass because when this is exposed to too much heat, it might break down and shatter. Iron is also not recommended as it may have the tendency to melt when the heat becomes too strong.