Most modern synthetic liners are engineered to stay flexible even in very cold conditions, so brittleness is far less of a concern than it once was. Materials such as reinforced polyethylene (RPE) or high-quality HDPE are formulated to handle sub-freezing temperatures without cracking, provided they are installed correctly and not exposed to sharp stresses.
Cold weather can make any material stiffer, but well-designed liners maintain enough elasticity to move with the surrounding soil as it contracts and expands. The biggest risks usually come from improper anchoring, heavy ice movement, or sudden impact on a frozen surface rather than the liner material failing on its own.
