Nispira high quality, effective HEPA filter helps to purify the air by capturing particulates. Particles 0.3 microns and larger that pass through the filter are captured to help maximize comfort and freshness. Activated carbon removes any unfavorable household odor such as cooking, smoke, pet smell, VOC chemical etc. This filter is compatible with the following Holmes air filter units: HAP242-NUC, HAPF300AH-U4R, HAPF30AT-U4R, CAP531-U, CAP529-U, HAP240, HAP242, HAP412, HAP422, HAP424, HAP706, HAP716, HAP9240, HAP9242, HAP9412, HAP9414, HAP9422 and HAP9424. It can also be used with the following Bionaire units: BAP260, BAP815, BAP825, BAP9200, BAP9700 and BAP520. It measures 1.2 x 10 x 4.6 inches and comes in a pack of 2. We recommend replacing your air purifier filters every 6 months to maintain effectiveness and efficiency. This is not a Holmes OEM product. Holmes is a trademark or registered trademark of its respective holder. Use of it does not imply any affiliation with or endorsement by the holder. The trademark holder is not affiliated with Nispira and does not endorse this product. Any use of the name Holmes or model Aer1 designation for this product is made solely for purposes of demonstrating compatibility.