It's called "honeycomb." Two sheets of aluminum bonded ("glued") to
(usually) aluminum foil honeycomb. Very strong and light in weight for
its strength. The filler can also be plastic honeycomb or rigid foam,
balsa wood, paper honeycomb (very much like corrugated cardboard on end),
and several other materials.
Some folding tables have a paper honeycomb top with Formica or melamine
like sheet for the top surface and a rough grade of similar material for
the underside.
You might be able to have a single one piece sheet made up for a
shell-off reflooring project. Different suppliers have different maximum
sizes.
"KMA offers assembly services, so you don't just buy a panel, you buy a
sub-assembly. All you need to do is secure it in place. We attach
moldings, hinges, locks, tapping plates, and anything else you can glue,
screw or fasten to a panel. You come up with what you need assembled and
we'll figure it out." www.kmamax.com
The aluminum will dent but any dents can be filled with a hard putty like
floor leveler or body putty and smoothed level. A sheet of 1/4" plywood
could be glued to the top surface to provide more puncture resistance,
but of course it will add weight. Maybe that cork flooring others have
mentioned would be good.
Rigid foam sheet that is integral with a hard skin on both sides is
available. It's not glued together - the foam core blends into a solid
skin on each side.
Years ago the airlines had fits over spike heels as they would ding the
floor of the aircraft.
So any such flooring should have an upper surface that it rigid and
strong enough to prevent denting.
Al