The right thickness of pool liner is a balance of strength and flexibility. If your liner is too thin it won’t stand up to regular wear and tear and if it’s too thick it won’t fit properly in tight corners or over complex shapes. A thick liner is also darn heavy, making it more difficult to install. Pool liner thickness is measured in “gauge” or “mil,” and they aren’t equivalent. A 30-mil vinyl liner is thicker than a 30-gauge liner so make sure you’re comparing apples to apples (or mil to mil!). We recommend a 27-mil (often referred to as a 30-gauge) liner for most applications.