(8) Application. The recommended application method for most foam filter oil is to completely saturate the foam and gently squeeze out the excess. Some filter oil comes in a spray can that goes on with the press of a button, but beware of trying to gain performance with a light coat. It will work, but it may cost you. Fabric filters can use spray-on oil or a spouted bottle to place a bead of oil on each pleat. K&N actually has a chart for the optimal quantity of oil for each filter based on surface area.