-Lint buildup: A+ The wider opening keeps the lint flowing through my 15-foot duct, and the duct will not need cleaning for quite a while. Fuzzies of lint occasionally build up under the flap door and keep it from closing fully. However, they soon blow away, and the vent appears to remain pestproof in this state.
https://www.amazon.com/Tec-Products-Inc-NPVW-Roducts/dp/B0032Y7EQO