Flubber is very easy to make. Put 1 1/2 cups of warm water into a pail or other container and add 2 cups of white glue. In a second container, mix 1 1/3 cups warm water and 3 tsp. of borax. Mix each container well, pour the contents of the second container into the first container and mix again. You can also add food coloring at this point just for fun. Knead or stir until all the liquid is absorbed and the mixture looks thick. Note that borax can be irritating to the skin and should never be swallowed, so always wash your hands after working with it.
White glue contains a chemical called polyvinyl acetate. This chemical is made of very long molecules called polymers that tend to get tangled together, which is why glue is so thick and viscous. The borax reacts with these long molecules to create what are called crosslinks, or bonds between the long molecules. The result is an even thicker mixture that behaves in special ways. The change produced by adding the borax and making the crosslinks can be demonstrated by comparing the original white glue with the finished Flubber. Flubber is much tougher and more viscous; you can even write on it with a marker.
Most fluids, such as water, flow perfectly well no matter how fast we try to move them along. These are called Newtonian fluids, named after the great scientist Isaac Newton. Some fluids, though, become more viscous and harder to move the faster we try to move them. These are non-Newtonian fluids, and because Flubber is one, it's a perfect material to illustrate this strange phenomenon.
To show this effect, pick up a handful of Flubber and spread your fingers. The goo will slowly ooze through your fingers and drip down like liquid honey. Then take a lump of Flubber and hold one end in each hand. Quickly pull your hands apart; the Flubber should snap like a solid.
The slow, steady flow of a block of Flubber can be used to show how glaciers, which are solid blocks of ice, can "flow" during an ice age. Make a block of Flubber about 2 by 6 inches and draw a line with a marker halfway down the top face, going from side to side. Place the block on an inclined board and leave it for an hour or so. During this time, the Flubber will slowly move down the board. The marker line will also show that the middle of the block moves more quickly than the sides. This can be used to illustrate how glaciers can flow even though they are solid.