Gloop, or Oobleck, is just a mixture of corn starch and water. Gus had a great time mixing the two and adding water to make it runny or corn starch to thicken it up. You know you have the right consistency when you can roll the gloop in your hand and make a solid ball. Then when you open your hand the ball melts into a gooey mess. It is a great way to show solids and liquids.
You can add food coloring or paint to make it different colors. Or even freeze some colored water to watch the colors mix as the ice cubes melt. If you mix corn starch, water, and baking soda together it also makes the same gloop consistency, but if you sprinkle a kool-aid packet on top the gloop will fizz and bubble. That was pretty cool.
The boys played for hours. Clean up was super easy.
For the library program I had different kinds of gloop set up at tables for the kids to play with. I also made some gloop by boiling water and cornstarch which made slime. The kids were able to spoon the slime into a strainer and watch as it oozed into the bowl below. Lots of fun.