Det nämns kort i filmens novellisering. Det är uppenbarligen en "konserverande / petrifierande gel".
Preservative gel began to fill the cells, spurring the condemned rebels to panic. Tor-An pounded uselessly at the translucent walls of his sarcophagus, while Faora screamed in rage. Nam-Ek required a larger cell than the others, but even his mammoth fists were unable to break through the rectangular force field that contained him
...
Lara watched as the petrifying gel congealed, revealing the rebels, frozen within their cells—as immobile as statues. They were preserved in various states of fear and anger. A look of utter malice contorted Zod’s rigid features.
Med ingen ytterligare beskrivning av vetenskapen bakom den tror jag att vi säkert kan anta att gelén till stor del består av renaste plotonium, ett sällsynt element som endast används av författare.