Reflecting heat: Aluminum foil has excellent heat reflection properties. By laying aluminum foil-coated insulation materials (such as aluminum foil insulation cotton, honeycomb aluminum foil panels) under building walls, roofs, and floors, it can reflect radiant heat. In summer, it can block outdoor heat from entering the building, and in winter, it can reduce heat loss from the interior, achieving the goal of energy conservation. HVAC: Used for the external covering of insulation layers for ducts and insulation for pipes to reduce energy loss. 

Aluminum foil is widely used in the field of building insulation and heat preservation. Its core principle lies in the high reflection performance of aluminum foil towards heat radiation. There are three basic ways of heat transfer: conduction, convection, and radiation. Aluminum foil mainly provides effective protection against heat radiation. When used in combination with other insulation materials, it can significantly enhance the overall insulation and heat preservation effect of the building. 

The main application forms of aluminum foil in building insulation and heat preservation: 

Aluminum foil insulation rolls/plates 

Structure: This is a common form. Usually, it is made with traditional insulation materials such as glass wool, rock wool, polyethylene (PE) foam, polystyrene foam (EPS/XPS) as the core material, and a single or multiple layers of aluminum foil are attached to the surface. 

Application: 

Wall insulation: Used in external wall insulation and internal wall insulation systems, it is laid between the base layer of the wall or the insulation layer. 

Roof insulation: Installed beneath the roof structure layer or above the insulation layer. 

Floor insulation: Installed beneath the ground concrete layer to prevent heat from escaping downward. 

Function: 

Reflective heat radiation: In summer, when the sun's radiation passes through the roof or walls, the aluminum foil can reflect most of the heat back, preventing it from entering the room; in winter, the heat radiation emitted by warm objects inside the room is reflected back into the room by the aluminum foil, reducing the loss of heat outward. 

Combined with the core material: The core material is mainly responsible for blocking heat conduction, while the aluminum foil enhances the barrier against heat radiation. The combination of the two results in a better effect. 

2. Aluminum foil bubble film / honeycomb aluminum foil sheet 

Structure: The aluminium foil is combined with the air layer in the middle. The bubble film is made by forming plastic (usually polyethylene) into bubble shapes, with aluminium foil attached on both sides or just one side; the honeycomb aluminium foil sheet is made by forming aluminium foil into a honeycomb structure. 

Application: 

Interlayer insulation: Commonly used in areas such as ceilings, partitions, and gaps around doors and windows. 

Pipe insulation: Wrapping around the exterior of heating or cooling pipes to reduce energy loss. 

Lower layer of the roof: Placed beneath the roof tiles, serving as an auxiliary insulation and heat preservation layer. 

Function: 

Reflective thermal radiation: The aluminum foil faces the direction of the heat source and reflects thermal radiation. 

Air layer insulation: The stationary air layer in the middle is itself a very good thermal insulator, which can effectively reduce heat conduction and convection. 

3. Thermal insulation of the HVAC system 

Application: Used for wrapping the supply air pipes, return air pipes, refrigerant pipes, etc. of central air conditioning systems. 

Function: 

Preventing condensation: The insulation layer can prevent the outer surface temperature of the low-temperature pipeline from being lower than the dew point temperature, thereby avoiding condensation. 

Reduce energy loss: Whether it is transporting cold air or heating, the insulation layer can reduce the heat exchange between the cold/heat medium inside the pipeline and the outside environment, thereby improving energy utilization efficiency. 

4. Reflective Insulation Coating / Roll Material 

Application: Although not pure aluminum foil, some reflective insulation materials incorporate or attach aluminum powder or very thin aluminum foil to the coating or roll material. 

Application: Applied by brushing or pasting on the roof and exterior wall surfaces. 

Function: Directly reflect solar radiation and reduce the surface temperature of buildings. 

Advantages and disadvantages of aluminum foil in building insulation: 

Advantages:

High-efficiency reflection: The reflectivity of heat radiation is extremely high (up to over 95%), resulting in remarkable heat insulation effects. 

Lightweight: Compared to traditional insulation materials of the same thickness, materials containing aluminum foil are usually lighter. 

Moisture-proofing: The aluminum foil itself does not absorb water and can play a certain role in moisture prevention, protecting the internal insulation core material. 

Durability: Chemically stable, does not age easily. 

Construction convenience: The sheet form is easy to cut and lay. 

Disadvantages: 

High thermal conductivity: Pure aluminum foil has excellent thermal conductivity on its own. However, if not installed properly (such as with gaps or damages), it can form a thermal bridge, thereby accelerating heat transfer. 

Prone to damage: The aluminum foil is relatively thin and is prone to being scratched or torn during the construction process, which can affect the effect. 

Installation requirements: Its performance is highly dependent on the correct installation orientation (the aluminum foil surface should face the heat source) and tightness. 

Summary

In the field of architecture, aluminium foil mainly achieves insulation and heat preservation by reflecting thermal radiation. It is rarely used alone but is combined with traditional insulation materials such as glass wool and foam plastic to form composite materials, which are then used in wall, roof, floor and pipeline insulation systems. Correct selection and installation of insulation materials containing aluminium foil can effectively reduce building energy consumption and enhance living comfort.