The ULC does not come into contact with the front glass unless intentionally pressed to touch the glass or is taking a blow from dropping the lens. Dirt, by default, does not come with your packaged ULC. If dirt, fine sand or debris enters in the inside of the ULC, there is no need to worry. We’ve already infused a special coating into the material of the ULC, making it so any collected finely grained silent killers (dirt, sand, debris, etc.) can be washed off and dried, looking brand new, within seconds.