If you use a cover, you must use a pillow of some sort to support the cover and, hopefully, have water flow off it. The water/ice in the pool acts as a support because otherwise the ice, snow and water in the cover puts a ton of inward pressure on the pool walls and can bend and collapse them. The ice on the top of the pool water is no big deal. In fact, if you keep your pool open the ice will keep debris from going to the bottom.
Watermom does not cover her AG pool over the winter. Other AG pool owners don't either. My dad used to use 6 or 8 truck inner tubes as his "bubble" and they worked great.
So the job of the pillow is to support the cover against ice and snow.
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