Lifetime Warranty against seam separations. 3 Year Full Warranty on non-seam issues, then 25 Year Pro-Rated Warranty on everything else.
Typically if a liner were to ever have a manufacturing defect, it would be in the seams, which on these liners have a 100% Lifetime warranty.
The Truth About Liner Thickness
Above ground pool liners are generally marketed and sold by a thickness standard called gauge. Gauge is not a set number but is a truly relative number and liner manufacturers that use this measurement are allowed to determine which gauge they want to use for stating their liners' thickness.
The truest measure of a pool liner is done using an international standard of mil thickness. This is an absolute fixed measuring system. Just like an inch is an inch, so to is mil thickness.