You can’t microwave popcorn twice because most of the popcorn kernels that are capable of popping, do so after the first round of microwaving. If you try to microwave the bag again, you’ll just risk burning the popcorn that’s already popped! This in turn will lead to the problems we’ve covered off in this article already - namely, unpleasant odors and potentially harmful substances.  Any kernels that didn’t pop the first time around are highly unlikely to do so at a second attempt. They simply lack the moisture and other conditions needed to pop!