When I started my last fruit fly culture I was out of coffee filters. I don't drink coffee and so it was a separate purchase for me. I got lazy and decided to cut up a pizza box I had readily available. Ten days later I had the biggest producing ff culture I have ever had. I have used large leaves, excelsior, and coffee filters in the past and found that the filters held up the best. However, cardboard was amazing! The cardboard had become saturated with the juices in the culture and I had more maggots than I had ever seen, and obviously more flies!