While the brilliant Reed Richards, leader of Marvel's Fantastic Four, is perhaps best known for the incredible stretching of his body, in one brutal fight with the Hulk the extent of Richards' impressive elastic abilities is on full display. Reed Richards gained his power of super elasticity through exposure to cosmic rays, along with Sue Storm, Johnny Storm, and Ben Grimm, while the three were piloting a spaceship early in their careers. Since then The Fantastic Four have fought countless enemies, with Reed's superior intelligence and superhuman stretching powers often allowing the team to gain the upper hand.
When assessing the strength of a Marvel character - or the upper limits of their abilities - one of the easiest and most reliable sources of information come from their battles with the Hulk, one of the physically strongest entities in the Marvel Universe. On the surface Mr. Fantastic's stretching abilities seem almost limitless, with the powerful hero able to form his body into almost any shape, turn into a liquid-like form, and even take most physical attacks without suffering any damage. This was on full display in Reed's battle against Hulk in Contest of Champions 2. This story saw the Hulk attempting to assault Richards with his fists and Reed not only being able to evade the punches, but also absorbing their blasts with little harm when Hulk did make contact. While Hulk eventually beat Mr. Fantastic by inhaling his entire body within him, this defeat did not show the upper limits of Reed's powers, which were not fully shown until the tumultuous events of World War Hulk.
This 2007 event sees Hulk returning to Earth for vengeance against the Illuminati after the secretive group - including Richards - exiled Hulk into space, with the Hulk also believing they are responsible for the death's of his wife and child. As with pretty much any battle that Reed Richards takes part in, he attempts to defeat Hulk first by using his massive brain to the power signature of Hulk's friend the Sentry in an attempt to pacify him. This plan is quickly foiled by the shockingly un-savage War Hulk. Of course, Reed does not give up, and in World War Hulk #2 by Greg Pak and John Romita Jr., he immediately attempts to stop Hulk's rampage by restraining him with his stretching. This is an inadvisable course of action that immediately fails because of how anger-empowered the Hulk is at the time.
Even Mr. Fantastic's Impressive Stretching Has Its Limits
Hulk is easily able to rip Mr. Fantastic off of him. Because of the incredibly high levels of rage-induced strength Hulk is experiencing, he smashes Reed with a massive "THRAKKADOOM!" that renders the impossibly stretchy man unconscious and unable to re-stabilize his stretched out form. Clearly there is a limit to Reed's stretching, and even though he has shown time and time again that his power of elasticity is able to make him invulnerable to most physical attacks, when going up against a Hulk who thought Reed killed his family, his powers are no match for the sheer brutal strength of the angered super being.
Reed's limits have been shown other times as well, such as when the shock of a blast from The Fantastic Four's nemesis Doctor Doom rendered his body so rubbery that he was unable to control it, but Reed Richards' defeat at the hands of Hulk in World War Hulk may be the ultimate display of his upper limits as a hero.