Umm sorry, I do not agree with the above statement.
why then do they not wrap expol, or do they not wrap the poly that is layed into concrete for insulation. water has no effect on poly!!!!
Fish bins are made of polystyrene, the get filled with water, yet the polys insulating characteristic does not change.
why do you think it is used for disposible cups.
Following extract taken from Expol website
www.expol.co.nz
Polystyrene Insulation has excellent thermal insulation properties essentially because it consists of mainly stabilised air.
It is a durable, non-irritating, inert organic material which will not rot and is highly resistant to mildew
No nutritive value to ants or rodents
Suffers little or no effect from water or water vapour. Even under the most adverse and rare conditions of total prolonged saturation it maintains its shape, size, structure, cohesion and physical appearance. The effect on the insulation value is minimal