Balloons are no longer just for birthday parties. Companies are creating air-filled works of art that can cost thousands of dollars.

Party City, the national retail chain, says it plans to close 45 stores this year. That’s about triple its typical rate of store closures. Sales have been declining, but the stores are also suffering from a global shortage of helium. That’s not the kind of thing you want to run out of when nearly 20% of your business comes from pre-filled balloons and helium tank rentals.

On the other hand, air is free, and people in the balloon business have gotten very good at cashing in on it.