The thickness of a flat wall does not explain all heat transfer through a container. Corner joints, metal fittings and door seals can interrupt the insulation path. Air leaking around a lid also carries heat; this is separate from conduction through solid material.
Points to inspect
Check insulation continuity at corners, fittings around hinges and frames, and seals for compression or dirt. See whether the door closes evenly at every point. Photograph visible damage and record its location and inspection date.
Compare with a temperature difference
When there is a temperature difference between inside and outside, measure the same surface points with a contact sensor or use a thermal camera in suitable conditions. A camera shows surface temperature; one image alone does not prove heat-loss quantity or food temperature. Record the time, inside and outside conditions, and surface location together.
If the door leaks, address cleanliness, closure and seal condition first; then repeat measurements under the same conditions. This lets you compare the repair's effect using a traceable record.
