I'm standing in a Costco store, and they have a large walled off area for chilled produce. The entrance to this section is a square opening about 10 feet on a side. When you walk in, you notice a rapid change from room temperature to cold.
I've noticed that this temperature barrier is extremely thin. You can stick your arm in and feel your hand is cold while your elbow is warm. How does this even work? There is a moderate current of air moving across the entrance as well so I'm sure that's the key. But with no differing materials on either side like a glass door to insulate it, what stops the heat from spreading over a wider area? Is moving air alone an insulator? Even if convection is prevented, what about conduction?