The present invention relates generally to a patch including a micro fiber glass and a polymeric binder, where the mixture forms an in situ porous patch that allows for active filtration after application to a leak or hole in an air filter. The mixture can be pressurized with a propellant within a housing prior to application to a leak or hole in an air filter. The mixture can also be applied manually to a leak or hole in an air filter, without the need to be pressurized with a propellant within a housing.