Above Floor pool parts were at one time designed exclusively of metal or metallic alloys. These days, the pool walls are still steel but nowadays maker's like Doughboy and Wilbar (Seaspray Pools) are working with resin elements in many in their models to boost their strength, sturdiness and merchandise longevity. https://www.profi-poolwelt.de/3-60-x-1-25-m-aufstellpool.html