Overview
- On Thursday Hannah Fry posted an Instagram video to her more than two million followers demonstrating the step-by-step trick of opening the rear window on the opposite side and quickly opening and closing the driver’s door.
- Fry explains the mechanism as bulk flow, where the moving door sweeps hot air out and the open rear window draws in cooler outside air.
- She says the technique takes about two to three rapid door cycles to work and is quicker than using the air conditioning, which she estimates can take roughly five minutes to cool the cabin.
- Mainstream UK outlets have widely amplified the video during the current heatwave but the coverage contains no independent testing or official endorsement of the method.
- Fry also suggests covering seats with blankets while the car is parked so the blankets absorb heat and can be removed before driving, a practical tip that could help people enter a cooler car without immediately running fuel‑using aircon.