Landfill liners are engineered barrier systems placed at the base and sides of a landfill to prevent the migration of leachate and harmful gases into surrounding soil and groundwater. They play a crucial role in the safe disposal of wastes by isolating solid waste from the natural environment and minimizing risks to public health and ecosystems. As waste decomposes in a landfill, liquids percolate through the waste mass and dissolve organic and inorganic contaminants, forming leachate. If uncontrolled, leachate can contaminate groundwater and surface water resources. Landfill liners are therefore designed to act as low-permeability barriers that control the movement of these contaminants and support sustainable waste management practices. The primary functions of landfill liners include containment of leachate, protection of groundwater, structural stability of the landfill, and compliance with environmental regulations. An effective liner system must possess low hydraulic conductivity, chemical resistance, durability, sufficient strength to withstand stresses from waste loads, and compatibility with site-specific conditions such as soil type, climate, and nature of waste. Modern landfills generally use composite liner systems rather than relying on a single material, as no single liner material alone can provide complete protection over the long term. Landfill liners can be broadly classified based on the material used and the structural arrangement of the liner system. On the basis of material, liners are commonly classified into natural liners, synthetic liners, and composite liners. Natural liners are made from naturally occurring materials with low permeability, primarily clay and clayey soils. Compacted clay liners are one of the earliest forms of landfill liners and are still widely used, especially where suitable clay is locally available. Clay liners function by restricting the flow of leachate due to the very small pore spaces in clay minerals. The effectiveness of a clay liner depends on its thickness, degree of compaction, moisture content, and mineral composition. Typically, compacted clay liners are constructed in multiple layers to achieve a very low hydraulic conductivity. However, clay liners are susceptible to cracking due to drying, freezing and thawing, differential settlement, and chemical attack from aggressive leachate, which may reduce their long-term performance. Another type of natural liner is amended soil liner, where native soil is mixed with materials such as bentonite to improve its impermeability. Bentonite-enhanced liners combine the swelling properties of bentonite with local soils to achieve lower permeability than natural soil alone. These liners are often used