Fujin coffee bags with valve one-way degassing valves are designed to allow pressure to be released from an airtight package while not allowing external atmosphere (i.e. air with 20.9% O2) to enter the package. 

The coffee bag gussets expand when the package is filled with product, and the weight of the product usually holds the bag upright. This coffee sack package format has two long faces, or panels, on the front and the back for product branding.