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 fragrances to choose from. We recommend choosing Black Ice, New Car, 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 a longer-lasting effect.