Microwaves: The Black GridWhy the metal screen has holes that block heat

From the show

Why it looks like that

The perforated screen on your microwave door is a precise engineering filter known as a Faraday cage. Its holes are calculated to be significantly smaller than the 12-centimeter wavelength of microwaves to reflect radiation back inside, yet large enough to allow tiny visible light waves to pass through. This design ensures safety without sacrificing your ability to monitor the food.