These Duct Mufflers use commercial grade acoustical neoprene foam made specifically for sound deadening. They're fully assembled, high-performance, and when connected to your fan and ducting, reduce your noise. These Duct Mufflers use commercial grade acoustical neoprene foam made specifically for sound deadening. They're fully assembled, high-performance, and when connected to your fan and ducting, reduce your noise output by up to 25dba without reducing airflow. Duct Mufflers are both non-toxic and fire resistant.