The MEB refrigerated-vehicle module asks for K ≤ 0.32 for bodies carrying goods frozen at -18 °C and below and K ≤ 0.40 W/m²·K for chilled carriage, and says these values are generally reached with 80 to 130 mm of polyurethane at 38-40 kg/m³. In ATP the upper limit is 0.40 (class IR, and classes E and F for mechanically refrigerated equipment); 0.32 is a design value.
The same line comes first in a comparison of the two arrangements: which thickness, which density, which measurement.
The wall's share is small. On a body of 72 m² surface with +30 °C outside and -18 °C inside, K = 0.32 lets 0.32 × 72 × 48, about 1.1 kW, through the wall; the module's 210 W/m³ for 24-40 m³ comes to about 6.9 kW on 33 m³; the coefficient includes door and defrost loads.
Thickness has a price: 130 mm instead of 80 mm takes roughly 10 cm from internal width and height. So thickness is chosen against the target temperature; ask in the quotation whether the K value was established on the finished body and at what thickness.
