Air-conditioning units on planes known as “packs” work by taking hot, pressurized “bleed air” from the plane's engines and cooling it down by using the cold temperature outside the plane at cruising altitude — which can be minus-40 or lower — before pushing it through the cabin.

Yes, planes naturally "cool down" because the outside air temperature at cruising altitudes (30,000 to 40,000 feet) is typically between -40°C and -60°C. However, the aircraft itself must be heated to keep passengers comfortable. In 2026, this is managed by the Environmental Control System (ECS). The system takes "bleed air" from the hot jet engines, which is often over 200°C, and runs it through "air cycle packs" (essentially massive air conditioners) to cool it down to a usable temperature. This cooled air is then mixed with recirculated cabin air to maintain a steady temperature of around 22°C to 24°C. Interestingly, the cabin can actually feel too warm during boarding in 2026 because the plane is packed with people (who generate heat) and the ground cooling units may be less efficient. Once in flight, the challenge for the ECS is balancing the freezing exterior cold with the internal heat generated by electronics and hundreds of human bodies to prevent the cabin from becoming uncomfortably chilly.