Winter ice pillow physics

[garymadaras]

Despite growing up with a large inground pool ( never using a winter pool pillow), this will be my first year as an adult winterizing an large oval above ground pool. I can’t understand the necessity of a pool pillow. Yes the pool will freeze. Yes ice expands. But there is nothing preventing the ice from expanding upward. Ice will not expand laterally and apply great force against the pool wall. It will expand up because there is no resistance. For example, cut the top of an empty soda can, fill half way with water and freeze. The ice just expands up. It does not burst the can. Makes me think the whole pillow concept is just another tactic by retailers to make more money - especially when their primary point is “they’re not expensive, why risk your $10k pool.” Can anyone enlighten me about why the ice wouldn't just Expand up? Thanks

[Denniswiseman]

The idea of the pool pillow is to keep the pool cover from filling with rain water