>>102368581
>>102368632
The bag is typically partially folded when it is placed in a microwave, and inflates as a result of steam pressure from the heated kernels.

Microwave popcorn bags are designed to avoid popped-kernel scorching, an undesirable effect that takes place when popped kernels are heated above 300 °F (150 °C).[1] A susceptor—usually a metalized film laminated onto the paper of the bag—absorbs microwaves and concentrates heat at the film interface, thus ensuring a heat distribution focused on the hard-to-heat flavor coating so that the unpopped kernels are evenly coated prior to popping, thereby ensuring even flavor throughout the product.