Rotomolded coolers are heavier due to their construction and materials. These coolers are made using a rotational molding process that results in thick, sturdy walls for enhanced durability and better insulation. The use of high-quality materials, like dense polyethylene, contributes to their weight, ensuring they are rugged and capable of retaining ice for longer periods. While the weight may be a downside for portability, it is a trade-off for their superior performance and durability.