When insulating around the pond will it make a difference wether using open cell or closed cell insulation. I am wondering about the static pressure collapsing the open cell against the sides of the walls over time.

I am considering using the 2 inch open cell polystyrene and was wondering if this will collapse to less than an inch and allow the liner to touch an errant screw or nail that is not properly set and if it could cause a tear.

This is on a QT tank 10L x 5W x 4D 2 feet above ground.
Is this a concern or am I worrying about nothing?
Do I need to use closed cell and make it 2inch by using overlapping sheets of 3/4 inch to achieve 2 1/4 inch?

Any one who has torn down a pond with this insulation notice any problems using the open cell type?

I will probably be building in the next week or so. I would appreciate comments or any experience with using this insulation.

Thanks
Charlie