I will be installing a new liner on a 27' round above ground pool. I have not decided whether to use an expandable liner, or a standard beaded liner. I'm thinking about digging down the floor and using an expandable liner to give the pool a deep end. My question is, how are the expandable liners constructed? Do they have extra material that simply follows the shape of the deep end (and therefore causes wrinkling on the floor), or do they actually stretch like a balloon to the shape of the deep end? If they stretch, then why couldn't a standard liner be used? Is the material for beaded liners actually different material than what expandable liners are made out of? If there simply is extra material available to pull into the deep end, and no expansion is occurring, then why are they called expandable? Most of the expandable liners seem to be 20 mil. The less expensive beaded and overlap liners are 20 mil, but the better ones seem to be 25 mil. I find it interesting that the expandable liners never seem to be made out of the thicker material. If the expandable liners are designed to actually stretch and expand to the shape of a deep end, is there a specific shape that they are constructed to best support? Would they support a gentle concave shape that started from the walls of the pool and was deepest in the center as well as they would support a deep end that started in the middle of the pool and "dropped off" to the 3/4 point of one end? Confused yet? Thanks!