<p>Compressed natural gas (CNG) is increasingly used as a cleaner fuel, creating a need for storage systems that balance structural integrity, weight, and safety. This review focuses on polymer-based composite materials and functional architectures employed in advanced Type III and Type IV CNG storage vessels. Polymer-based composite systems are discussed, with emphasis on factors such as gas permeation, fatigue-induced damage, and interfacial degradation that govern their performance. Nanocomposite materials such as graphene- and MXene-reinforced systems are also examined. The effect of polymer–nanofiller interactions in enhancing mechanical performance and barrier characteristics is given special consideration. Furthermore, the capacity of self-healing polymer structures to repair microcracks and enhance long-term durability is investigated. An alternate method of low-pressure storage is briefly discussed: adsorbed natural gas (ANG) systems. The review also highlights how artificial intelligence-based diagnostics and IoT-enabled sensors are being used for early leak detection, predictive maintenance, and real-time monitoring in gas storage systems. Overall, this review integrates advancements in composite vessel design, polymer materials, and intelligent monitoring technologies to offer insights into potential future paths for safer and more effective CNG storage systems.</p> Graphical abstract <p></p>