Harrington’s thumb rule states that for every 1% increase in seed moisture content (SMC), seed lifetime decreases by 50%. Thus, to avoid post-harvest grain losses, stored seeds must be insulated from water. Although the jute bags typically used to store grains afford an ecofriendly, durable, and low-cost storage solution, their hydrophilic nature makes them vulnerable to wetting from airborne humidity and precipitation events. To address this issue, we treated jute fabrics with alkali and wax to render them water-repellent. A 2-month seed storage experiment revealed that wax-coated jute bags (WCJBs) outperformed control jute bags (CJBs) at safeguarding wheat (Triticum aestivum) grains exposed to 55%–98% relative humidity. Specifically, grains stored in WCJBs exhibited 15%–50% less SMC than grains stored in CJBs, which led to a 21%–66% enhancement in the germination efficacy of WCJB-stored seeds. This engineering solution could enhance the potential of jute bags to reduce post-harvest losses.