Yes it was just the white, lightweight type of stuff.
Used quite thick size, might have been 2 inches thick.
Presumambly it should never see a load except it's own weight and any wind forces on it.
I think it has been used in the other bigger Harrys for also making part of the cockpit roof.
And of course also in the sacrificial bows too.

Ineterstingly i ride body or boogie boards and thet must see pretty intense loads at times. Some of the makes, like the Australian Manta boards are made with white polystyrene looking foam. Perhaps it is a higher grade than ordinary packing and stuff.
Other bodyboards have another type of foam which always seems fairly heavier to me, i forget the names, i think P.E. which is polyethylene? Was one sort used in like the Morey Boogie boards.
The boards tend to lose their stiffness and become more bendy as time goes on.
They have no glass on surfaces, but do have a semi-solid plastic slick glued or bonded onto the bottom.

Doug