As it freezes and expands, water in above-ground pools can make the walls crack. Pool pillows for above-ground pools are a solution: inflate the pillow to 60–70 % of its full capacity so that, as freezing progresses, the impact of expansion goes to squeezing the pillow instead of into the walls. Plus, if you put a pool cover on top, the bulging pillow will prevent the accumulation of precipitation and debris at the center: lower risk of collapse!