Join Date: Feb 2000
Location: Annapolis, Md
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Nothing, unlike less expensive foams normally used on power boats and airex is a cross-linked closed cell foam so the water stays pretty much within that localized area where it got access. There is a slight exception to that in areas with a large number of freeze thaw cycles, where the melting and refreezing water can cause a delamination between the foam and the skin. Unlike Balsa this is a pretty easy repair accomplished by drilling holes, draining the area, drying it out and injecting with resin.
The nice thing about airex is that it has a little bit of memory which greatly increases impact resistance over a non-cored hull.