These high quality liners are designed to fit above ground pools with dug-out hoppers. Hopper Liners differ from traditional expandable liners in that they are tailored to fit specific dimensions. Hopper liners are installed according to a 'dig sheet'-- a special diagram detailing the exact dimensions to dig the hole during pool installation. Each hopper liner is made to conform precisely to the specifications of its corresponding dig sheet. Uni-Bead construction.