Swimming pools are either lined with a plaster to waterproof the outline of the pool or they are lined with vinyl swimming pool liners.  The vinyl pool liners are custom made to fit into any sized swimming pool, and come in many different colors, designs and thicknesses.  These pool liners also come in a number of styles, such as beaded or overlap.  The difference in vinyl pool liners is the way they attach to the swimming pool wall upon installation.  A beaded pool liner will snap into a track at sits near the top of the pool wall and an overlap pool liner actually overlaps the pool wall and is held down by coping.  These liners are usually installed over sand, but swimming pool stores do sell a pad that can replace the sand when installing the liner.  However, these vinyl swimming pool liners do not last forever, so you will need to replace it every 10 years or so.  Vinyl lined pools are the most common and least expensive types of swimming pools for the US, but the concrete pools work just as well.