U-value is measured in watts per square metre per kelvin (W/m²K). A lower U-value means less heat leaks through. R-value is its inverse, in m²K/W, and higher is better. For a single material, R-value equals thickness divided by thermal conductivity, so 100 mm of foam at 0.022 W/m·K gives an R-value of about 4.5 and a U-value of about 0.22.
These numbers let you compare walls of different materials and thicknesses. The same 100 mm of EPS gives an R-value under 3, so more heat flows through each square metre. Multiply the U-value by the wall area and the temperature difference between inside and outside, and you have the transmission heat load the refrigeration system must handle.
Temperature difference is where India's climate shows up. A freezer at −20 °C in a 40 °C room has a 60-degree difference across its walls, roughly double that of a chiller in an air-conditioned shop. Thicker or better insulation pays back quickest where that difference is largest.