You should first confirm the air purifier model name to find which filters are compatible with your unit. You can find the model number on the label inside the top cylinder of the air purifier. In some air purifiers, this is located directly at the back of the air purifier.
If your Blue Pure air purifier is cylindrical, carefully rotate counter-clockwise the top cylinder and remove it from the unit. Underneath the top of the air purifier, you will see a sticker with a barcode on it. You can find the model and serial number on the same sticker.
If your Blue Pure air purifier is square, gently press the buttons simultaneously on both sides of the unit. Lift off the top of the team. Underneath the top of the air purifier, you will see a sticker with a barcode on it. You can find the model and serial number on the same sticker.
Once you know your model number, you can go to https://www.blueair.com/us/air-purifier-filters. Scroll down and select the model you have. All compatible filters and pre-filters will then be displayed. You can then click and order your filter as needed.