Doubtfire

All atoms are more than 99.99% space, so everything we are aware of in the universe is almost completely empty space.
That take the wind out of your sails?

Yeah because lead is obviously lighter than this microlattice. /s

"Oh, your 300mph supercar isn't so fast, don't you know the earth is flying through space at 67,000mph?"

But alright, you are a very clever boy for pointing out the irrelevant-obvious.

A more interesting question/comment about this is its strength. Aerogels are quite strong, and have a number of other outstanding properties such as their utility as an insulator. It looks like this material (or "structure", since it seems to me more akin to miniaturized scaffolding) has a completely different set of pros and cons than aerogel so it greatly increases our palette of options when it comes to ultralite construction -- quite useful for aerospace and many other industries...