This is the Pre-filter for the GC air purifier. This GC HEPA Pre-Filter (F1) is a powerful HyperHEPA pre-filter which eliminates micro- and nano-particles such as allergens, smoke, bacteria and viruses. Media consists of non-woven microfiber, mini-pleated for high-capacity, non-off gassing separators. Average filter life: 18 months (based on average daily usage of 10h on speed 3).