As another top-level comment mentioned, depending on the sheer strength, it could be used in composite structures.

Take a 2'x2' 1" thick piece of foam. Laminate some fiberglass onto both sides of it. This is basically how modern boat hulls are constructed. Extremely light, rigid, insulated and durable.

WAG, but if it would allow you to replace 1 ton of foam on a 40' yacht, that's one ton of extra cargo/amenities you could carry instead and maintain the same water line. Or alternatively you could produce a faster boat with less wetted area.

I'm sure a real engineer has a better idea of practical applications. But I like cruising yachts so. :-)