The noise reduction elbow, the ZWA erect pipe elbow muffler series and the ZWB type horizontal elbow muffler series adopt the centrifugal glass cotton as the sound absorbing material, the inner circular structure form part of the product, and the wind absorbing sound sheet in the middle of the elbow. The inner circular structure has the advantages of simple structure, large noise reduction and small resistance. The centrifugal glass cotton has the characteristics of stable sound absorption, uniform density, easy making and so on. It has the characteristics of waterproof, mildew proof, and moth proof. It is incomparable to other sound absorbing materials.