Gelatin

It may sound like an oxymoron, but Solid Liquid is by definition solidified liquid. Nobody knows exactly what types of compounds make up this perhaps supernatural element. The best way to describe it is "pale gelatin". It looks like a drop of water but Pikmin are not harmed by it. Instead, it knocks them back if they come into contact with it. This can be troublesome if there is a barrier infused with Solid Liquid, or if spheres of Solid Liquid fall while you're in the middle of a battle. Fortunately, Purple Pikmin can make Solid Liquid susceptible to damage if they are thrown at the element. It will turn purple and can be beaten to pieces.

Trivia
Solid Liquid is the substance that makes up the Waterwraith's body.

Further Trivia
Solid Liquid is actually a pun on the names of two major characters in the "Metal Gear Solid" series; Solid Snake, the protagonist, and Liquid Snake, generally the antagonist (later "Liquid Ocelot.")

Portal- Kombat