Expandable pool liners are simply very tall overlap liners. Extra big to ensure adequate material exists to accommodate deeper swimming areas. Some expandable liners allow for up to 3 feet of additional water depth, making typical above ground pools up to 7 feet deep. Deep ends and deep centers are created by dishing out the pool floor to the desired shape and depth prior to installing the expandable liner. These liners conform to your unique pool floor shape. Trim off excess material if needed.