What's in the walls of the refrigerator: structure, materials and design secrets

When you open the refrigerator door to get milk or vegetables, you see only the inner lining of the chamber, shelves and boxes. However, behind this simple plastic panel lies a complex engineering system that maintains low temperatures for years. Many users do not even think about what is inside the walls of their household appliance until they are faced with a breakdown or the need for transportation.

Inside the case there is a multi-layer structure, reminiscent of a sandwich, where each layer performs a strictly defined function. From thermal insulation to refrigerant pipes, all elements work in unison. Understanding the device helps not only to take better care of equipment, but also to quickly diagnose faults that may arise during operation.

Modern models can differ significantly in their internal architecture depending on the type of defrosting system and energy efficiency class. In older models, you could see simple foam and open tubes, while the newest No Frost systems hide the evaporator deep inside the body. Let's look in detail at what exactly this “filling” consists of.

Multilayer structure of the case: outer and inner layers

The outer shell of the refrigerator is the first barrier that protects the insides from mechanical damage and moisture. It is usually made of sheet steel coated with special powder paint. This material was not chosen by chance: it is scratch-resistant, easy to clean and does not rust when exposed to atmospheric humidity. In premium models, instead of metal, tempered glass or stainless steel with a special coating can be used Anti-Fingerprint.

The inner layer that you see when you open the door is made of impact-resistant plastic. Most often it is polystyrene or ABS plastic. Polystyrene it is characterized by high rigidity and smoothness, which makes it easier to maintain, but it is more fragile at low temperatures. ABS plastic is more elastic and shock-resistant, but can turn yellow over time under the influence of ultraviolet radiation if the refrigerator is located near a window.

Between the outer metal and the inner plastic there is the most important thing - the thermal insulation layer. It is this that prevents the cold from evaporating outside and the heat from penetrating inside. The thickness of this layer can vary from 3 to 6 centimeters depending on the energy efficiency class of the model. The thicker and better the insulation, the less often the compressor turns on, saving your energy.

⚠️ Attention: Damage to the outer metal casing (dents, through scratches) can disrupt the tightness of the thermal circuit, which will lead to the formation of condensation inside the wall and corrosion of the metal.

It is important to note that the connection The formation of the inner and outer layers occurs not mechanically, but chemically during the foaming process. This creates a monolithic structure, which also acts as a load-bearing element. Hull rigidity directly depends on the quality of the foam material inside.

Thermal insulation: the role of polyurethane foam in maintaining cold

The main material that fills the space between the walls is polyurethane foam (PPU). This is a gas-filled plastic that foams directly in the confined space of the refrigerator body. In liquid form, the components of the mixture are poured into the gap between the outer and inner casing, where they react, increase in volume and harden, forming a dense foam.

The uniqueness of polyurethane foam lies in its cellular structure. Millions of microscopic bubbles filled with gas prevent heat transfer. The gas used in foaming has a thermal conductivity significantly lower than that of air. Over time, this gas can be replaced by air from the environment, which slightly reduces the effectiveness of insulation, but modern technologies make it possible to minimize this process.

Foaming quality is a critical parameter. If the technology is broken, voids or “cold bridges” may form inside. In such places, condensation or even frost may form on the outer wall of the refrigerator. Single-component two-component PU foam systems provide different densities and adhesion to metal.

In addition to thermal insulation, polyurethane foam serves as a sound absorber. It dampens vibrations transmitted from a running compressor and fan motor. Without this layer, the refrigerator would operate much louder, transmitting a hum through the metal body.

Hidden cooling system: evaporators and tubes

The most interesting part of the “filling” is the refrigerant circulation system. In old-style refrigerators operating on a static system (drip defrosting), the evaporator was often a coil frozen directly into the back wall inside the chamber or located behind it. In modern models No Frost everything looks different.

In “No Frost” systems, the main evaporator is hidden in a separate compartment, usually in the upper part of the refrigerator compartment or behind the back panel of the freezer. It is there that the fan drives cold air through special channels, which are also laid inside the walls or behind plastic panels. You don’t see ice on the products because it accumulates on the hidden evaporator.

• ❄️ Aluminum plates —the main material for heat exchangers, since aluminum has high thermal conductivity.
• 🌬️ Fans —ensure the circulation of air masses inside the hidden cavities of the body.
• 💧 Drainage tubes - remove melt water from the hidden evaporator into the tray above the compressor.

Tubes with freon pass through the entire perimeter of the refrigerator. Often the first part of the circuit (discharge) is laid inside the side walls or around the perimeter of the doorway. This is done in order to use the heat from hot freon to heat the seals, preventing them from freezing and the formation of condensation at the ends.

Why are the side walls sometimes hot?

The side walls can heat up to 50-60 degrees Celsius in the first hours of operation or during intensive loading. This is a normal process of heat removal from the condenser, which is often built into the sidewalls.

The tightness of this system is the key to the long life of the device. Any microcrack in the tube running inside the polyurethane foam will lead to gas leakage and loss of cooling capacity. Repairing such systems requires opening the case, which is often not economically feasible.

Electrical components and control systems

Behind the plastic panels lies not only hardware, but also electronics. In simple models, this is a mechanical thermostat with a capillary tube, the end of which is located in the chamber. In complex modern units, temperature sensors, defrost sensors, and even control modules are hidden behind the walls.

Capillary tube The thermostat is a thin copper conductor filled with a temperature-sensitive gas or liquid. When the temperature inside the chamber changes, the pressure in the tube changes, which mechanically opens or closes the compressor contacts. Damage to this tube (for example, due to careless defrosting with a knife) disables the thermostat.

In systems No Frost defrost heating elements are added. They are located directly on the hidden evaporator. When the sensor detects icing, the compressor turns off and the heating element turns on, melting the ice. This entire system is hidden behind the back wall inside the freezer.

All electrical connections are carefully insulated and protected from moisture, but condensation inside the case is the main enemy of electronics. This is why the integrity of internal partitions and drainage systems is so important for safety.

Dangers when the internal walls are damaged

Many users try to defrost the refrigerator themselves, using a knife or other sharp objects to chip the ice. This is a serious mistake. Breakdown of the internal wall camera leads to instant depressurization of the cooling system. You will hear the hiss of escaping gas, and the refrigerator will stop cooling.

Electrical wiring elements can also pass inside the walls, although this happens less often. Damage to wire insulation in high humidity and low temperature environments can result in a short circuit. In the best case, the fuse will burn out, in the worst case, there will be a risk of fire in the polyurethane foam, which, despite the flame retardant additives, is a flammable material.

⚠️ Attention: If you break through the wall and feel a strong chemical smell or hear a hissing sound, immediately unplug the device, ensure the room is ventilated and call a technician. It is not enough to seal the hole with tape yourself - the system has lost its tightness.

Another hidden danger is a violation of the geometry of the case. A strong blow to the outer wall can compress the internal freon circulation channels or deform the evaporator. Visually this may not be noticeable, but the performance will drop, and the compressor will begin to wear out.

Environmental friendliness and modern materials

The question of what is inside is also important from an environmental point of view. Old refrigerators manufactured before 2010 often contained type freons, which destroy the ozone layer. Modern models use R-12which destroyed the ozone layer. Modern models use R-600a (isobutane) or R-134a. Isobutane is safe for the ozone layer, but is a flammable gas, which imposes special requirements on the tightness of the system.

Polyurethane foam of modern refrigerators has also become more environmentally friendly. Gases that do not contain chlorofluorocarbons (HFCs) are now used to foam it. This reduces the carbon footprint of equipment production and disposal. However, when old refrigerators are burned in landfills, all these materials release toxic substances, so proper disposal is mandatory.

Manufacturers are constantly looking for new materials for internal plastic, adding antibacterial additives. Silver ions or copper components are introduced into the plastic structure to suppress the growth of bacteria on the walls of the chamber. This is especially true for models with a function Zone Fresh or similar freshness zones.

When choosing a new refrigerator, you should pay attention to the energy efficiency class, which directly depends on the quality of the “filling” of the walls. Class A++ and A+++ models have more advanced insulation and an optimized circulation system, which, in terms of 10 years of service, will save a significant amount.

Is it possible to replace the seal yourself if it is frozen? wall?

You can replace the seal, but if it is frozen, under no circumstances tear it off by force. Defrost the mounting location naturally or use a hairdryer at the lowest temperature so as not to melt the plastic of the case. Damage to the sealing area will disrupt the seal of the chamber.

Why does the inside of the refrigerator smell like plastic after purchase?

The new smell is caused by the release of volatile substances from the fresh plastic of the inner case and polyurethane foam. This is fine. It is recommended to wash the chamber with a weak soda solution and ventilate the refrigerator for 1-2 days without food. If the smell does not go away for a week, this is a cause for concern.

Is polyurethane foam inside the walls dangerous for health?

When frozen, high-quality polyurethane foam is absolutely inert and safe. The only danger is the combustion process or strong heating with an open flame, when the material begins to release toxic gases. Under normal operating conditions, it does not pose a threat.

What to do if ice has formed inside the wall?

Ice inside the wall (bloating) indicates a violation of the tightness of the thermal circuit or moisture getting into the insulation. This leads to metal corrosion and destruction of polyurethane foam. Diagnostics by a technician is required; it may be necessary to open the wall to dry and seal the leak.

Is it possible to paint the interior walls of the refrigerator?

It is strictly not recommended. Conventional paints are not intended for food contact and low temperatures; they can crack and begin to release harmful substances. In addition, a layer of paint will worsen the thermal conductivity of the evaporator if it is built into the wall.