The expandable liners measured in Mil thickness are more of a "Heavy Duty" liner which is suited to work any steel wall above ground pool user looking for a deeper pool experience. These liners can expand up to either 60" or 72". You'll have plenty of backyard fun with a deeper pool this summer. All liners are comprised virgin vinyl material making them the top contender.
Liner Mil thickness is an actual international measurement standard that can be measured with a micrometer. Liner Gauge thickness is a arbitrary measurement with no international measurement standards.
15 Mil liners are generally thicker than 20 gauge liners
20 Mil liners are in ground pool liner thickness making them the thickest above ground liners on the market.
Expandable liners are not expandable in the sense that they stretch. Expandable liners have a specific fixed maximum detph. They are made of vinyl material that is only made to slightly stretch due to its pliability. The term expandable liner originates from the concept of a flat bottom above ground pool. Taking a flat bottom pool mindset and expanding it to have a slightly deeper swim area.
Several years ago there were only flat bottom above ground pools. A fixed depth if you will. Then a liner was designed that would allow the flat bottom concept to be expanded to include a deeper area for swimming. Thus the birth of expandable liners. Today, the expandable liner depths now vary from 60" to 72" depending upon the liner manufacture.