Karatand;
“
...a Karatand... It was in effect a palmless glove made of impact-sensitive plastic about a quarter-inch thick. Pressed, pinched, drawn on or off the hand, it remained flexible and nearly as soft as good leather. Struck against a resistant surface, its behavior changed magically, and while the interior stayed soft to act as a cushion against bruising, its outer layers became as rigid as metal.
He thrust his fingers into it and spun around, slamming his fist at the wall. There was a solid thud, and the muscles of his upper arm and shoulder complained, but the Karatand reacted as designed. It was several seconds before he could straighten his fingers against the resistance of the relaxing plastic.”
That sort of material behavior occurs in real life under rare circumstances.
Corn starch, water, and one or two other ingredients, when combined in the right proportions, will instantly (but temporarily) harden when hit with high force, but otherwise allow your hand to easily move through the substance if not at a high attack speed.
I had the opportunity to witness this at an event at a university engineering campus.