100% food grade PE raw material production, environmental certification by SGS. Adapted and installed in coffee bags, and some fermented food bags. When the air pressure in the system is greater than the outside air pressure, will be through the exhaust valve of the gas system is discharged to go, while blocking the outside air in order to undermine the quality of the food aroma. It is equivalent to the exhaust port to install a one-way valve. Exhaust gas system can go through the check valve, and gas adsorption not come outside.