We have been using a 20x25x1 1500 filter for years. We have 6 indoor cats and it does catch a lot of dust and hair. However, in the last year the filters we have been using do taco (fold inward and bend) even within days of replacing. By the time we replace it has developed a concave shape. We buy our filters in packages of 6 to save money since they are pricey, but we like how they perform at cleaning the air. In the past they did not do this until this last group of 6 filters. Each of them has cleaned the air well but I am concerned about the bending.