How do hermetic or airtight bags work to keep stored grain pest free?

Hermetic or airtight storage works on a simple idea: seal the grain so almost no air can move in or out. Insects and the grain itself keep breathing inside the sealed bag, which slowly uses up the oxygen and builds up carbon dioxide. In that low oxygen condition the insects cannot survive or breed, so an infestation dies down without any chemical. This only works well if two conditions are met. First, the grain must be properly dry before you seal it, otherwise you trap moisture and risk mould. Second, the bag or container must be genuinely sealed and filled with little air space, and free of holes from rats or rough handling. These bags are sold as triple-layer or similar hermetic liners, often used inside a normal sack. They are reusable for a few seasons if handled carefully and are widely reported to protect grain and pulses for months and to keep seed viable. For a small farmer they are usually worth it because they cut both insect losses and the need for chemicals. Check rates and availability with your KVK, FPO or local supplier, and confirm safe drying moisture before sealing.