They permit airflow to move in a single path and to circumvent it in the opposite way. These are built from corrosion resistant extruded aluminum. All zinc-plated steel components is changed with stainless steel, protecting hardware from rust and corrosion when subjected to higher humidity or large humidity environments. A https://zanderashvj.howeweb.com/37627339/detailed-notes-on-heavy-duty-stainless-steel-damper-manufacturers