Plastic fan backdraught shutter

Plastic fan backdraught shutter non return check valve for better ventilation purpose prevent insects and smoke Features: 1. Made of ABS plastic, which is antistatic and ageing resistant. It can keep away distortion for a long time. 2. The outlet sizes choice : 100mm, 125mm, 150mm, 200mm, etc. Benefits to set this product to the ventilation pipe: prevent outside air from penetrating the home. prevent the smoke from public pipe enter into the home. prevent insects fly or climb