We looked for something similar to the wall foam sold for pools, any alternative that work work in the same way. We just could not find it. Like Insomnix said, you don't need it but I'm here to tell you that we have had without, and with our last liner replacement we added it - MUCH nicer and even though it may be incrimental, I do believe it adds a bit of insulation property. I'm glad we added it this time around.