A hydrogel is a solid, jelly-like material that can vary from soft and weak to hard and tough. By weight, gels are mostly liquid, yet they behave like solids.
Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects.
Here are some simple activities to show demonstrate a few of the properties of hydrogels.
(Revised version with 2 new experiments - 17/02/2014)