>The surface doesn't appear to be sealed, so I imagine the aerogels are saturated with air.
>
>That would be analogous to wood - most woods are less dense than water and therefore float, but not if they're saturated with water i.e. waterlogged.

Good reply, it is definitely a better way of explaining it, rather than having to go into the complexities of specific gravities, intertial mass, intermolecular bindings & Van Der Waals force.