The 3 F eliminate a sound layer, the adoption eliminate an asbestos silk to draw up and eject you air of voice decline to 5 decibel the following, lower than the voice of your heart palpitates.

• 第三层是消音层，采用消声石棉丝编制，将你排出气体的声音降到5分贝以下，比你心跳的声音还低。