Foamed Metal is what you're thinking of. It was supposed to be one of the "killer-apps" for space/microgravity manufacturing. The idea has been around since the mid-20 and is a staple in manufcturing on Earth:Back in the 90s I read about scientists trying to create what I will call metallic snow or styrofoam. Would be incredibly strong and very light and barely conduct heat.
The idea was to find a way to get a more uniform and greater volume (total) of gas inot the metal matrix by working in free-fall.
In free-fall melted metal would have gas injected that would creat micro-pockets making the metal exctremely light yet just as strong as the regular metal. Since the gas pockets would be so small and if exposed to vaccum before the metal cooled fully would then contain an insulating vaccum, thermal conductivity was greatly reduced. Or so the theory went anyway. Practical tests showed you need some way to get uniform distribution of the gas in teh metal and that was difficult to achieve at the time. ((Tests tended to get several large voids instead of small pockets)