Because of this, originality consists in returning to the origin.
Antoni Gaudi (https://www.brainyquote.com/quotes/quotes/a/antonigaud291537.html)
I reread Armageddon 2419. As I've been told to be original it is best to return to the original (Winchell Chung told me but credited Gaudi.) More on inertron.
Inertron is mostly inert. It is opaque to electromagnetic radiation. It does not interact with normal matter actually repelling and being repelled by it. These properties make it a perfect thermal insulator since heat can't be passed by radiation, conduction or convection. It has a great molecular density apart from its reverse weight. It is a structural element in some vehicles (the spines of two man fighters the North Americans use). It is not as hard as steel and a hacksaw will cut through it fairly easily.
The Americans in the story made frequent use of small amounts of inertron to lighten equipment, especially their artillery. Another popular use was a blanket with inertron fibers in it to let it retain heat better. Inertron might come in different grades (in terms of lifting power) and hardness and flexibility.
A room shielded with inertron would be bug proof. Buck says specifically that inertron has no molecular motion and technically exists at absolute zero. It won't feel cold because it won't draw heat from your hand. It would also block infrared emissions, though you'd have to let that heat out somewhere, sometime or roast.
This is great for lining rocket chambers. If inertron repels matter from direct contact with it then you have a containment device for antimatter (thanks to Winchell Chung for the suggestions.) It could also be an excellent shield against neutrinos, better than lead, allowing you to build small and light (!) fission reactors. Inertron could also speed fission reactions by reflecting neutrons back into the radioactive fuel.
Then we have inertron's ugly cousin who seems to get no love, only Avengers related jokes -ultron.
Ultron never made it to the comic strips as far as I could see. It was also a synthetic and exotic matter. While inertron was opaque to radiation ultron was perfectly transparent and said to be a perfect conductor. Ultron partitions were a safety hazard because people would keep walking into them. Like inertron it was very dense and also incredibly strong. We are shown at one point that a five mile long length of invisibly thin ultron wire could still support the weight of five grown adults (they took their jump belts anyway.) It could also be alloyed with other metals to tint it as desired.
Besides making windows to endanger birds, ultron is a room temperature superconductor (it might also conduct heat with equal ease making it vital for heat disposal systems. It is said to have perfect magnetic response meaning maglev propelled vehicles become a breeze. But more importantly the metal and its two derivatives allow the manipulation of ultronic radiations and this will give the user a vital edge in any exploration, surveillance, and conflict.
Ultron could emit and absorb ultronic particles, what we would call quarks these days. An ultronic battery could be made using metultron (emitter) and ketultron plates and using inertron as an insulator. The ultron particles could flow between the plates as a current or be beamed.
Ultronic particles (waves, wavicles? Dunno) act similar to EM but are almost unaffected by passage through normal matter. You could focus beams of ultronic radiation on a spot and create an emission point or glowspot. This could give you a monochrome view of the scene if you caught the emitted rays on an ultron screen (scan-o-tron or ultron-o-scope or something similarly diesel punk sounding). It could also provide x-ray vision (without damaging rads!) if you set the receiver right. Color ultron vision was probably a few years away when the book was written (give or take 500 years).
Ultron could be made into microphones to convey sound. This revolutionized communications that previously depended on someone using a marker and whiteboard. Presumably inertron could shield from ultronoscopes and broadcasts.*
Ultronics allowed a group to operate without using radio waves. Radio, television, radar all had ultron equivalents and they were completely untraceable to a force that didn't have ultron technology. Worse, the ultron equipped forces could jam the entire radio spectrum to deny their enemies use of radios or radar. All the while they could continue scanning and chatting using ultron. If you can't win an otherwise hopeless fight with that kind of advantage you just aren't pulp hero material.
A lot of the technology in Armageddon 2419 is our stuff made smaller, faster, and more accurate. Fabrication of exotic matter is the magical part of it, something we wouldn't even guess at now. We're sort of like Victorians figuring out how the Sun generates its heat. As a science fiction novel it falls very much into here is this invention, what can we do with it? It deals with futuristic technology letting Americans wage a war of liberation against an enemy occupying their land and oppressing them (all without central production, a transport system or mass production in place or needed).
*Yes. I wrote that with a straight face and I'm going to own it.