What kind of foam will work under the liner????

[scootchu]

I have a 27' AG round pool and the liner is tired and leaking and will be replaced. I have read the posts in the forum about various foam bases under a liner. I already have sand, but like the thought of a flat foam bottom. If I smooth the sand and remove some for use as coving can I use 1/4" or 3/8" fanfold? I see that happy bottom is only 1/4". When I do research online it seems as though even 1/2" Dow blue board is equal in price to using Happy Bottom. Also could laminate foam underlayment be used for the pool walls???
Scott

[MarkC]

I used 1/2" carpet padding under a liner in my old above ground pool. The blue foam board may dent and not bounce back like a carpet pad like foam would. Try denting a small piece and see if it returns to normal. It would still probably be OK with the denting but just might end up collecting dirt in the depressions.

[scootchu]

I used 1/2" carpet padding under a liner in my old above ground pool. .

Was that directly on the ground/sand? Won't it rot or just become nasty when damp?