There are often layers or many layers of aluminum foil included in insulating materials. In actuality, a simple radiant barrier can work effectively with only one sheet of aluminum foil. It may seem odd to utilize metal as an insulator given how well metals carry heat, especially aluminum. This is how it goes.

Fundamentals of Heat Transfer

The energy of the atoms in a material can be measured in terms of heat. The temperature of the substance increases with their energy level. Three methods are used to transfer this energy: via radiation, convection, and conduction

Thermal energy is passed through a substance during conduction. The energy transfers quickly when atoms are closely packed, as they are in a solid metal.

Either infrared or visible light. The sun emits light, some of which travels through the atmosphere and is absorbed by things like plants, soil, and water.

Taking Up Radiant Energy. Certain materials do better than others at absorbing light and energy. Wood and concrete absorb a significantly higher percentage of heat than does bright material like aluminum, which tends to radiate a lot of heat. This means that when exposed to radiant heat, metal doesn't heat up quickly.

Because aluminum foil doesn't radiate heat into the environment, it can be a useful insulating material. It will warm up through conduction from the shingles, which is what makes it beneficial directly under a roof, but it won't radiate that heat into the attic area. For instance, in HVAC applications, the foil prevents heat from entering or escaping, maintaining the desired temperature inside the ducts. Numerous additional household and commercial applications make use of the same idea.

Then based on these, people created Aluminum foil bubble or foam insulation material, as we known these product can help us to keep warm/cold and save energy, bring us a lot of convenience.

Now you can understand the working principle of Aluminum foil, good job!