One good reason to choose plastic protective vents is safety because metal has sharp edges. Plastic vent doesn't have seams, rivets and welding. These give less potential for water to get in, or for an installer to injure themselves. What's more, plastic protective vents won't lead to more condensation with temperature changes. And also, the plastic protective vents won't corrode and rust. http://www.srlvents.com/protective-vents/plastic-protective-vents/