Most carbon air filters are manufactured from granulated activated carbon (GAC), which is used either as loose-fill within a filter housing, or bonded into carbon blocks. Both methods have their particular advantages and disadvantages, but there are common misconceptions about bonded GAC filters - in particular that they have a reduced working life compared to equivalent loose-fill filters. Here David Jefferies, product manager for carbon filters at Interfilta (UK) Ltd, clarifies the comparison.