To decrease the flow of heat, thermal insulation is essentially insulation. It keeps the hot stuff hot and the cold stuff cold. Basically, insulation is anything which slowly conducts heat.
Heat is an energy source which flows from hot to cold. Water could flow from high places to low places, down from the top of a waterfall, just like that.
By trapping the heat in the house, or trapping your body heat within your clothes, insulation keeps you warm in winter. To know more, visit this website.
Yes, to keep your home warm in winter, you can use heaters or a fireplace. But if thermal insulation is taken into account when the building is built, you will need less energy to keep the temperature comfortably high. To insulate the floor, fibreglass batts or blankets may be used as fibreglass is a weak heat conductor. Cellulose or other loose fitting materials which trap air can be used by plugging up the nooks and crannies to seal in the heat in the building.
You will need less energy to heat up the house if the home is well insulated to hold the heat in and the cold out. Important savings in terms of energy will result. With the price of fuel these days, you would not only make wiser use of the earth’s energy, you would also save money in the long run.
As for thermal clothes, in the film The Day After Tomorrow, I keep thinking of the homeless man. He was unable to afford thermal clothes, but he knew how to stay warm for sure. By way of thermal insulation. He filled his clothes with newspapers, and paper is a bad conductor of heat. Body heat is then trapped under the newspapers, holding the man wet.