This is an air vent filter commonly found in rental apartments. I bought a lot of them, but I'm moving and no longer need them, so I'm selling them. The outer bags show some age, but the products themselves are new and unopened! Includes filters with lids and outdoor allergen block filters, sizes 16cm x 16cm and 21cm x 21cm, with 1 or 2 filters per pack. - Product Name: Allergen Block Filter - Size: 16cm x 16cm - Size: 21cm x 21cm - Quantity: 7 filters - Application: For air vents with lids - Application: For outdoor air vents Thank you for looking.