PU foam v groundwater. Problem? 

Watch your fingers with that blunt knife😊

i lined my pond with 100mm jab floor, side and bottom, 10 years of a 2m water column pressure made no impact on the polystyrene at all, i used a rubber liner so all pressure would be transmitted to jabfloor. I know this as i filled in pond when leccy prices started to go up.

M8, you hit the nail on the head when you said, "Where is their proof?" ,end of

What's the foam there for is it just for insulation