The Cardboard air freshener for cars will keep working for 7-10 days once opened and can be stored for 12 months unopened. We have over 30 fragraces to choose from. We recommended to choosing Pine, Lavender, Vanilla, Forest, Jasmine or Strawberry fragrances, as they come with a stronger fragrance. For other lighter fragrances, you can choose to add extra fragrance for longer lasting effect.