Refrigerator insulation materials work in much the same way as other types of insulation in that they help maintain temperature levels within an enclosed space. In effect, the insulation that lines the walls and cabinets of a refrigerator keep interior areas cold. Urethane foams and fiberglass are the most commonly used refrigerator insulation material.
In general, insulation materials carry R-value ratings that indicate a material’s ability to prevent heat from flowing through it. R-values run from R-7 to R-50 with the higher values providing the strongest heat resistance. The type of material, its thickness and its density determine its heat resistance capacity.
The cold conditions present within refrigerators tend to naturally produce moisture and condensation -- especially when heated or warm air makes contact with cabinet, wall and food surfaces. Moisture and condensation develop as warm and cold air molecules combine. As warm air molecules cool, they release water vapors. These vapors appear as condensation on exposed surfaces.
Moisture and condensation act as heat conductors, meaning moist, exposed surfaces naturally absorb and conduct heat. So, refrigerator insulation materials have a two-fold purpose in terms of keeping heat out and preventing condensation from forming.
Thermal Resistance Factors
R-value ratings for insulation consider a material’s thermal resistance capacity per square inch of material. Polyurethane foam insulation, in particular carries an R-value of R-7 to R-8 per square inch. And while an R-7 or R-8 value falls fairly low within the range of R-value ratings, the moisture and condensation factors inherent in refrigeration systems works best with a lower value insulation material. This tendency towards moisture and condensation tends to counteract any insulating effect in cases where a material has too high of an R-value.
Polyurethane foam and fiberglass materials have a tendency to trap air molecules within their textures. This quality makes for an effective refrigerator insulation material. Air, in and of itself, does not conduct heat very well so these materials create a natural barrier between refrigerator components and the outside air environment. Since metal materials conduct heat pretty easily, the air barrier created inside refrigerator insulation materials reflects the heat transfers that come through refrigerator wall surfaces. The less heat that enters a refrigerator compartment the less the system will have to work to maintain a cold environment.