Keep your air purifier running smoothly with the Winix Replacement Filter O. This 360 All-in-One True HEPA filter fits perfectly with Winix A231 A230 models, and is designed to last up to 12 months. The filter frame is made of durable plastic, while the filtration technology includes a carbon filter media that captures particles as small as 0.3 microns. This replacement filter is manufactured in Korea, and is an essential part of maintaining good indoor air quality. It's easy to install, and helps to remove allergens, bacteria, and other pollutants from the air. So why wait? Order your Winix Replacement Filter O today, and breathe easier knowing your air purifier is working at its best.