Foam Vs Sand for bottom?

Foam vs sand?
Breaking ground this weekend for my 16x48 pool! So level, foam board (or sand) and tarp?

Been searching for foam board vs sand for flooring. From my understanding foam replaces sand completely 9maybe a little sand for divots)? I plan on leaving it up year round, no snow just rain here (northern California) . Does foam board hold up to elements well? I know it's more pricey but $100 more doesn't really bother me. I just want something that will last. I see most using 3/4" to 1". How many sheets for 16'? I read 8 I believe...


I can't find this in my 94513 area

http://m.homedepot.com/p/Owens-Corni...-37L/100320340

What about (i heard the expanded wont hold up tho):
http://m.lowes.com/product?langId=-1...lue=4294858106