Non-drying sticky PBT-32 tackifier Exclusive dirt indicator dot Self sealing gasket to prevent bypass Heat sealed two stage filter to minimize flutter The Series 55 Intake Panel Filter is the Industry Standard in Cross Draft Filters. Often imitated but never duplicated, the Series 55 Filter Line from Viskon-Aire has the unique PBT-32 Tackifier which will NOT DRY OUT OR UNLOAD DIRT. This assures the shop that they will not spoil a great paint finish. Also a Viskon-Aire exclusive is the Dirt Indicator. The Dirt Indicator is a Heat Sealed Dot in the filter that will remain white while the filter loads with dirt. Over time the filter media will appear soiled, and the indicator will stay white, telling the shop personnel to change the filter. Heat sealed two stage filter to minimize flutter and self sealing gasket to prevent bypass.; If your customer is looking for the best filter for the money, it is the Viskon-Aire’s Series 55.