We at Vinyl Liner Direct prefer to speak in "mil", or thousandths of an inch. 20 Gauge liners purchased on various websites contain liners made from 10 mil to 12 mil materials. Therefore, the majority of aboveground liners sold are 17 mil materials, or 30 Gauge equivalency, or 20 mil materials for 35 Gauge equivalency.
Aboveground liners are backed by a one-year limited warranty by the manufacturer. The warranty does not cover staining, fading, etc. but does cover manufacturing defects, or where the liner is seamed together.