Aquascape Heavy-Duty Pond Underlayment is about 30% thicker than our Standard Underlayment, offering enhanced protection against rocky, root-filled, and uneven soil surfaces that could damage the liner. Despite its increased thickness, this underlayment spreads easily and features a non-slip surface, ensuring quick and easy installation. Made from soft polypropylene geotextile, it allows gases to escape properly, preventing them from becoming trapped beneath the liner.