In filter cassettes, numerous mesh layers retain the oil and grease particles and eliminate the smoke from the kitchen. The cassette filter is composed of aluminium or stainless steel. The cassette stainless steel filters are a bit more expensive than the aluminium ones. But cassette filters made of aluminium are easy to handle, lighter, and require careful maintenance. On the other hand, stainless steel models are hard to handle, bulkier, and are easy to clean. http://www.guidling.net/filter-cassettes/