A decrease in the efficiency of a household refrigerator is often associated not with a compressor breakdown or freon leak, but with banal wear and tear thermal insulation layer. Over time, factory insulation can cake, become saturated with moisture, or lose its properties, which causes the unit to wear out and consume excess electricity. In such situations, the owner is faced with the question of choosing a modern analogue, and extruded polystyrene foam is considered one of the most effective solutions.
However, simply buying the first sheet of foam plastic on the construction market is a gross mistake that can lead to a fire hazard or violation of sanitary standards. Extruded polystyrene foam (EPS or XPS) has a unique closed-cell structure, but different brands of this material differ radically in density, vapor permeability and, most importantly, in flammability class. For household electrical appliances operating in a closed circuit, these parameters are critical.
In this article we will analyze in detail which type of EPS is suitable for insulating refrigeration chambers, how to correctly calculate the thickness of the layer and what installation nuances must be taken into account so as not to disrupt the operation of the thermostat. You will learn why ordinary construction foam is categorically not suitable for this purpose and how to avoid common mistakes when doing DIY repairs.
Criteria for choosing a material for refrigeration equipment
When choosing thermal insulation for a refrigerator, the thermal conductivity coefficient, denoted as λ (lambda), is of paramount importance. The lower this indicator, the better the material retains cold. Extruded polystyrene foam demonstrates some of the best results on the market, but other physical properties are also important for refrigeration technology, which are often ignored by amateurs.
The second critical parameter is moisture absorption. Temperature changes constantly occur inside the refrigerator, which inevitably leads to moisture condensation. If the insulation absorbs water, its thermal insulation properties will drop to almost zero, and the metal body will begin to corrode from the inside. EPS has almost zero water absorption, which makes it an ideal candidate, unlike mineral wool or conventional foam.
⚠️ Attention: Never use materials that do not have a fire safety certificate for interior use as insulation for a refrigerator. When ignited, a closed volume creates the effect of an aerosol bomb.
It is also necessary to pay attention to the mechanical compressive strength. During operation, the refrigerator can be moved, vibration from the compressor is transmitted to the housing. The material must be rigid enough so as not to crumble and form voids through which the cold will escape. Cheap brands of low-density EPS may not withstand long-term vibration loads.
Flammability classes and fire safety
The issue of fire safety when using polymer materials in household appliances is especially acute. Most types of extruded polystyrene foam are classified as combustible materials, but their flammability varies. For use in the refrigerator body, where electrical components and potential sources of sparking are located, this becomes a decisive factor.
There are several flammability classes, but for our task two main ones are important: G3 (normally flammable) and G4 (highly flammable). When burning, materials of class G4 emit a large amount of heat and toxic smoke, and are also prone to the formation of burning droplets. The use of such material inside a household appliance is unacceptable according to fire safety rules.
The optimal choice is EPPS with flame retardant additives, labeled as G1 (low-flammable) or, in extreme cases, G2. Such materials are capable of self-extinguishing when the source of fire is removed. It is important to understand that even the presence of fire retardants does not make the material flammable, but significantly slows down the spread of the flame, giving time for reaction.
- 🔥 Class G1 - the material does not support combustion in the absence of a fire source, ideal for household appliances.
- ⚠️ Class G2 - moderately flammable, permissible only if there is an additional fireproof shell.
- ❌ Class G3 and G4 - are strictly prohibited for use in the internal cavities of electrical appliances.
- 💨 Smoke emission - pay attention to the index D (D1-D3); for refrigerators, D1 is preferable (low smoke generation).
When working with EPS, it is also worth considering chemical compatibility. Some types of polystyrene foam can break down when exposed to certain solvents, adhesives, or even oils that may be present in the cooling system. Therefore, the choice of adhesive composition for fixing the insulation should be as careful as the choice of the slab itself.
Comparative table of material characteristics
To finally make a choice, it is necessary to compare the technical characteristics of various brands of EPS on the market. Not all boards are the same: differences in density directly affect their insulating properties and mechanical strength. Below is a comparative table of popular types of materials.
| Parameter | PSB-S foam | EPS (standard) | EPS (high-density) | Mineral cotton wool |
|---|---|---|---|---|
| Thermal conductivity (W/m K) | 0.037 - 0.043 | 0.028 - 0.032 | 0.028 - 0.030 | 0.035 - 0.045 |
| Moisture absorption (%) | 1.0 - 3.0 | 0.2 - 0.4 | 0.1 - 0.2 | Up to 10 (without protection) |
| Density (kg/m³) | 15 - 25 | 25 - 35 | 40 - 45 | 30 - 50 |
| Class flammability | G3 - G4 | G2 - G3 | G1 - G2 | NG (non-flammable) |
| Service life (years) | 10 - 15 | 40 - 50 | 50+ | 10 - 20 |
From the table it is clear that extruded polystyrene foam it outperforms conventional foam in all key indicators, except, perhaps, price. High-density grades of EPS have the best dimensional stability, which is critical for a tight fit to the walls of the refrigerator without the formation of cold bridges.
Mineral wool, despite its non-flammability, loses in the ability to maintain properties in a humid environment. If the circuit depressurizes in the refrigerator or condensation forms, the cotton wool will instantly become wet and stop working. In this regard, EPS is much more reliable and durable.
Why is density important?
The density of a material directly affects its compressive strength. For a refrigerator that is stationary, this may not seem important, but low density means larger cells and poorer insulation. In addition, loose material is more difficult to properly glue to a metal wall.
Do-it-yourself insulation replacement technology
The process of replacing thermal insulation in a refrigerator requires care and adherence to a certain sequence of actions. First you need to completely dismantle the old insulation if it has become unusable. Often, older models use glass wool or compacted foam, which can be toxic, so work should be carried out with a respirator and gloves.
The metal surface inside and outside the case must be thoroughly cleaned of glue residues, dust and grease. For degreasing, it is better to use alcohol solutions, avoiding aggressive solvents that can damage the painted layer or plastic. After cleaning, the surface must be completely dry.
⚠️ Attention: Do not use acetone, toluene or gasoline-based adhesives for gluing EPS. These substances dissolve polystyrene foam, turning it into a sticky mass. Use polyurethane foam adhesives or special compositions for polystyrene foam.
New EPS should be cut with a small allowance of 2-3 mm to ensure a tight fit into the body cells. The slab should fit in with light force, filling all voids. For fixation, it is better to combine mechanical pressure (with spacers) and an adhesive layer applied dotted or in strips.
☑️ Checklist for preparing for insulation
After laying all the sheets, it is necessary to allow the glue to completely polymerize. This usually takes from 12 to 24 hours depending on the temperature and humidity in the room. Only after complete drying can you assemble the internal plastic lining of the refrigerator and connect the unit to the network.
Common mistakes when insulating
One of the most common mistakes is using too thick a layer of insulation. In pursuit of energy efficiency, craftsmen reduce the usable volume of the refrigeration chamber, which makes operation inconvenient. In addition, excessive thickening of the walls can disrupt the operation of the heat removal system from the compressor if the insulation blocks the ventilation gaps.
Another mistake is ignoring the vapor barrier. Although XPS itself is vapor-tight, the joints between the sheets and the junctions with the evaporator tubes require special attention. If you leave gaps, warm, moist air from the room will penetrate inside, condense on cold metal parts and cause corrosion.
Thermal expansion of materials is also often forgotten. Polymers have a high coefficient of linear expansion. If you fill all the voids with mounting foam “tightly”, during heating and cooling cycles the structure may deform, which will lead to cracks in the plastic or peeling of the internal lining.
- 🚫 Using ordinary office glue or PVA - they do not hold EPS on the metal.
- 🚫 Filling all the cracks of the mounting foam without taking into account expansion - the risk of deformation of the body.
- 🚫 Ignoring the ventilation of the engine compartment - overheating of the compressor.
- 🚫 The use of flammable materials without a fire retardant coating.
Frequently asked questions (FAQ)
Is it possible to use regular white foam instead of extruded foam?
Technically it is possible, but not recommended. Conventional polystyrene foam (PSB) has larger granules, holds its shape worse and is destroyed more quickly by vibration. Its thermal conductivity is higher, and moisture absorption is much greater, which in the long term will lead to the appearance of mold and rust inside the housing.
How thick should the EPS layer be?
The optimal thickness depends on the climate zone and the desired efficiency, but usually it corresponds to the thickness of the factory insulation that has been dismantled. Most often this is in the range from 30 to 50 mm. Increasing the thickness to more than 60 mm in household models does not make economic sense, since the increase in efficiency becomes minimal.
Is EPS safe for storing food?
The cured extruded polystyrene foam itself is chemically inert and safe. However, in the design of the refrigerator, it is located behind a plastic inner chamber and does not come into direct contact with the food. The main requirement is the use of materials with a flammability class of at least G2 and the absence of odor after installation.
Is it necessary to seal the joints of the sheets with tape?
Yes, this is a good practice. Using aluminum tape or specialized foil tape for gluing joints creates an additional vapor barrier and prevents air movement between layers of insulation, eliminating convective heat loss.
What to do if the EPS crumbles when cutting?
Crumbling of the material indicates its low quality or expired shelf life. High-quality EPS should cut smoothly, without the formation of a large amount of crumbs. For cutting, it is better to use a sharpened knife or a special string heated to a certain temperature to melt the edges of the cut.