Vari-Plus MERV 13 VPL-8504 #1117104 The Vari-Plus extended surface air filter is another superior product in the Airguard family of rigid high efficiency products. The unique design of the Vari-Plus offers a wide range of dirt removal efficiencies coupled with extremly low resistance to air flow. When compared to traditional rigid or cartridge style filters, the Vari-Plus provides between 40% and 300% more surface area, assuring long service life and economical operation. The Vari-Plus filters are constructed with microglass fiber paper media. The depth loading media is formed into mini-pleats which are seperated by continuous beads of thermo-setting adhesive.