Valve bags are among the most commonly used packaging solutions, particularly for products in powder form, such as flour, activated carbon, plastic pellets, and cement. A key feature of valve bags is the small opening or valve at the corner, through which the bag is filled. This valve includes an inner flap that acts as a self-closing check valve once filling is complete. Valve bags are available with either a plain valve or an extended inner sleeve made of paper or film. When an extended “tuck-in sleeve” is used, it is manually folded down and tucked back into the pocket beneath the sleeve for a secure closure, preventing sifting. In simple terms, once the bag is filled, the pressure of the contents inside automatically seals the valve, providing a self-sealing function.