In the film, Professor Chang says Infra-Man is powered by a nuclear reactor, but later on in it he seems to be inexplicably solar-powered (only Infra-Man's Solar Ray Weapon is powered by the Sun; the rest of him is nuclear-powered).
During several of the fights between the creatures and the Silver Suited Men in the film, several of them have tears in the crotches of their uniforms (which can be seen when the men land on their backs and their legs are not close together).
In the film when fighting the plant monster in the forest, Infra-Man grabs the monster to toss him over his shoulder. At this point, the back of the monster suit splits open, revealing a striped shirt underneath.
When Professor Chang fills his syringe in the film, you can see a good amount of air in it just before he makes an injection into Infra-Man. Our hero would have died of air embolism.
In the film, the Infra-Man suit works only with solar power; nevertheless, Infra-Man can still fight in the cave of the Underworld (again, only Infra-Man's Solar Ray Weapon is powered by the Sun; the rest of him is nuclear-powered).