A modern refrigerator is a complex thermodynamic system, where each element plays a critical role in maintaining low temperatures. The main barrier preventing the penetration of heat from the outside is the thermal insulation layer, which is hidden between the outer metal shell of the case and the inner plastic chamber. It is the quality and type of material used that determines how quietly the compressor will operate and how much electricity your unit consumes.
In the production of household appliances, engineers use materials with extremely low thermal conductivity, which are able to retain their properties for years without shrinkage and degradation. Thermal insulation does not just fill the space - it creates a sealed circuit that prevents the formation of condensation inside the housing structure. Understanding what exactly this layer is made of will help you better navigate the characteristics of models when purchasing or repairing.
Most modern models, whether compact Indesit or massive Liebherr, use the same principle of insulator operation. However, the chemical composition and structure of the foam may differ depending on the price segment and year of manufacture of the device. Let's look in detail at what exactly is inside the walls of your refrigerator.
Polyurethane foam: the main thermal insulation material
The absolute leader in the field of thermal insulation of household appliances is polyurethane foam (PPU). This material is a gas-filled plastic, which is obtained as a result of a chemical reaction of two components: a polyol and an isocyanate. During the production process, these liquids are mixed with a foaming agent, after which a violent reaction occurs with the release of heat and gas, which leads to an increase in the volume of the mixture tens of times.
The main advantage of polyurethane foam is its cellular structure. Closed cells the materials are filled with an inert gas, which has a thermal conductivity significantly lower than that of air. It is this gas that provides the main insulating effect. Over time, over many years of operation, gas can gradually be replaced by air, which slightly reduces efficiency, but the material continues to perform its function.
⚠️ Attention! Polyurethane foam in its liquid state is toxic and flammable. It is strictly forbidden to try to foam the voids in the refrigerator body yourself with household mounting sealant. Industrial polyurethane foam has a different chemical composition and cell structure.
Hardening foam has excellent adhesion to metal and plastic, which allows you to create a monolithic structure without cold bridges. After hardening, the material becomes chemically inert, does not emit harmful substances and has no odor. It is thanks to polyurethane foam that the walls of modern refrigerators can be relatively thin, while maintaining a high internal volume.
Expanded polystyrene and other alternative materials
Although polyurethane foam dominates the market, in some models, especially the budget segment or older modifications, can be found in polystyrene foam. This is a hard, lightweight white material, often called foam plastic in everyday life. It has higher rigidity, but is inferior to polyurethane foam in its ability to fill complex cavities without gaps.
In structures with expanded polystyrene, the insulating layer is often assembled from ready-made slabs that are inserted between the walls. This method is less effective because there are microscopic gaps between the plates and the walls of the chamber through which heat can penetrate. In addition, polystyrene foam is higher, which requires an increase in wall thickness to achieve the same energy efficiency indicators. Thermal conductivity In rare cases, for example, in some chest freezers or specialized storage equipment, glass wool or mineral wool may be used. However, this is practically not used for household refrigerators due to the hygroscopicity of the materials - they easily absorb moisture, losing their properties and causing corrosion of the metal. thermal conductivity expanded polystyrene is higher, which requires increasing the wall thickness to achieve the same energy efficiency indicators.
In rare cases, such as some chest freezers or specialized storage equipment, glass wool or mineral wool may be used. However, this is practically not used for household refrigerators due to the hygroscopicity of the materials - they easily absorb moisture, losing their properties and causing metal corrosion.
Why don’t they use vacuum panels?
Vacuum panels (VIP) have excellent insulation, but they are very expensive and are afraid of mechanical damage. They are used only in premium models for critical areas.
Dry Foaming technology and environmental friendliness
Modern production has switched to a technology known as Dry Foaming (dry foaming). Previously, freons were often used as a foaming agent, which negatively affected the ozone layer of the planet. Today, manufacturers are required to use environmentally friendly components, such as cyclopentane.
Cyclopentane is a hydrocarbon that does not destroy the ozone layer and does not contribute to global warming. However, it is highly flammable in liquid and gaseous states. This imposes special requirements on production processes: workshops must be equipped with powerful ventilation and explosion protection systems.
For the consumer, the transition to “green” refrigerants and blowing agents means that the new refrigerator is safe for health. The gases contained in PU foam cells are non-toxic. However, when disposing of old equipment, it is important to follow the rules so that the insulating material does not come into contact with an open flame, where it can release dangerous combustion products.
Comparison of the characteristics of insulating materials
To better understand the difference between the materials used in refrigeration technology, it is advisable to consider their physical properties in comparison. This will help to evaluate why manufacturers make a choice in favor of one or another component.
| Characteristics | Polyurethane foam (PPU) | Expanded polystyrene | Mineral wool |
|---|---|---|---|
| Thermal conductivity | 0.019–0.025 W/m K | 0.030–0.040 W/m K | 0.035–0.045 W/m K |
| Moisture absorption | Minimum (closed cells) | Low | High (requires protection) |
| Mechanical strength | High (monolith) | Medium (fragile) | Low (caking) |
| Ecologically friendly | Safe after polymerization | Safe | Safe (with a binder) |
The table shows that polyurethane foam wins in all key parameters critical for a refrigerator. Low thermal conductivity allows you to make the walls thinner, increasing the usable volume, and low moisture absorption guarantees the durability of the body without rust from the inside.
Polystyrene foam is more often found in the doors of some budget models, where structural rigidity is important, but even there it is often combined with polyurethane foam to improve insulation. The use of mineral wool in modern household models is almost completely excluded.
Design features of door insulation
The refrigerator door is the most vulnerable place in terms of heat loss, since it constantly opens and is subjected to mechanical stress. That is why increased demands are placed on the insulation in this zone in terms of strength and shape stability.
Inside the door panel, insulation is often combined with rigid plastic inserts or denser grades of polyurethane foam are used. This is necessary so that when attaching shelves, handles or door closer mechanisms, the material does not crumble or deform. Tightness the perimeter of the door is also ensured by the precise fit of the insulating contour.
⚠️ Attention! If you notice that the door has begun to sag or a dent has appeared in the corner, this may compromise the integrity of the inner layer of insulation. Condensation may begin to accumulate at the site of damage.
Often there are refrigerant channels inside the door (in models with a perimeter cooling system). The insulation here must be especially careful so that the cold is not transferred to the outer metal surface, causing abundant dew formation in humid days.
☑️ Checking the condition of the insulation
Problems and defects in thermal insulation
Despite its high reliability, the insulating layer may suffer. The most common problem is a violation of the factory filling technology, which leads to the formation of voids or “pockets”. In such places, heat penetrates inside faster, causing the compressor to work harder.
Another common defect is the separation of the internal plastic from the foam. This can occur due to sudden temperature changes or mechanical shocks during transportation. If you hear a characteristic crack or see swelling of the plastic inside the chamber, this is a sign of a violation of the adhesion of the layers.
In old refrigerators that are more than 15–20 years old, natural degradation of the properties of polyurethane foam may be observed. The material may shrink or crack slightly, resulting in increased energy consumption. In this case, replacing the insulation is not economically feasible; it is easier to replace the unit with a new, more energy-efficient one.
FAQ: Frequently asked questions
Is it possible to replace the insulation in a refrigerator on your own?
No, this is almost impossible at home. This requires special equipment for mixing the components under pressure, as well as a mold for pouring. An attempt to use a household cylinder with polyurethane foam will lead to destruction of the structure due to secondary expansion of the foam and loss of thermal insulation properties.
Why is the outside of the refrigerator warm, is this normal?
Yes, this is normal for many models. Condenser tubes often run through the side walls and give off heat. In addition, the insulation itself is not an ideal barrier, and some of the heat from the operation of the compressor can be transferred to the housing, especially in a hot room.
Is the smell of a new refrigerator harmful due to the insulation?
A slight technical smell in the first hours of operation is acceptable. It comes from new plastic parts and packaging. If the smell is pungent, chemical and does not go away after 24–48 hours of ventilation, this may indicate defective materials or a violation of production technology.
Does wall thickness affect the useful volume?
Absolutely. The use of modern highly efficient insulators allows you to make the walls thinner (technology Vacuum Insulation Panel or simply high-quality polyurethane foam), keeping the external dimensions standard, but increasing the internal space of the chamber.