Popcorn tastes best when it is fresh and crispy rather than soft and stale. So, while it's best to eat popcorn right away, you can preserve popcorn that's already been heated. By preserving the popcorn properly, just like the popcorn warming machines at movie theaters and other public places, you can be sure that your popcorn will remain fresh even hours later.
Pour the heated popcorn that you want to preserve into a bowl or container with a lid. This popcorn should be without any butter, salt or toppings to ensure that it doesn't get soft or soggy. Close the bowl or container tightly with the lid and set the popcorn aside. It will stay warm for a while, and will stay fresh even after it gets cool. Instead of a plastic bowl or container, you can also use a glass jar with a lid.
Place popcorn in its bag or in a covered bowl or container into the freezer. The freezer prevents the popcorn from becoming soggy, chewy or stale due to its cool temperature. As a result, the popcorn doesn't absorb any moisture, as it would absorb from the air, and remains crisp and fresh. When you remove it from the freezer, you can heat your popcorn in an oven for a few minutes, or leave it out in room temperature until it warms up.
Store popcorn for a maximum of one to two weeks. Do not keep it in a refrigerator, which has some moisture and may dry the popcorn out. Do not store popcorn outside or in a car for a long time either.
Keep popcorn away from moisture and humidity, since freshly popped popcorn tends to absorb the humidity quickly. As a result, it becomes soggy and soft. It's best to keep it in a dry, dark area.