Activated Carbon Register Vent Filtration - Each package contains 12 vent filters. Has a activated charcoal impregnated in a poly mat to help trap dirt, dust, smoke, pollen sized particles and reduce odor through furnace/AC registers. Keeps dirt & objects from falling into ducts. Can be trimmed to fit standard size vents --- 4" X 12" and under. Why use Register vent filters? Register vent filters are made of a self-charging electrostatic material attracts dust, smoke, pollen and other pollutants in your vent register system. Use in any room of your home or RV. When air flows through the filter, dirt, dust, smoke, and pollen sized particles are trapped. Filtered air then passes back into your house. Naturally reduces odors through your home. Keeps dirt and objects from falling into ducts. Vent filters are designed to provide filtered air in your home.These Filters are made in the US