Guitar Breath Sound Hole Cover Made of felt with a perforated structure, it "doesn't completely block, allowing breath (BREATH)" = natural muting. Easy to remove (just insert). - String tension remains almost unchanged. - Sometimes used to prevent howling during recording. Made of felt/sponge-like sound-absorbing material to: - Absorb air vibrations inside the guitar. - Reduce volume and bass resonance. When in use: Absorbs hand sweat, humidity, and dust, and the sound-absorbing performance may decrease or odors may develop, so the sponge (felt part) should be washed and reused.